Electrolyte and secondary battery

ABSTRACT

An electrolyte includes a solvent and an electrolyte salt. The solvent contains at least one selected from ester compounds, lithium monofluorophosphate, and lithium difluorophosphate, and at least one selected from anhydrous compounds. The ester compounds are chain compounds having ester moieties, such as (—O—C(═O)—O—R), at both ends. The anhydrous compounds are cyclic compounds having, for example, a disulfonic anhydride group, (—S(O═) 2 —O—S(O═) 2 —).

CROSS REFERENCES TO RELATED APPLICATIONS

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-006441 filedin the Japan Patent Office on Jan. 15, 2009, the entire content of whichis hereby incorporated by reference.

BACKGROUND

The present application relates to an electrolyte containing a solventand an electrolyte salt and a secondary battery using the electrolyte.

In recent years, portable electronic devices such as video cameras,digital still cameras, cellular phones, and notebook computers havebecome increasingly popular. There is strong need for reducing theirsize and weight and extending their lifetime. Under such trends,development of batteries, in particular, secondary batteries, that canbe used as power sources, are small and light-weight, and achieve highenergy densities is proceeding.

In particular, lithium-ion secondary batteries that utilize occlusionand release of lithium ions and lithium metal secondary batteries thatutilize precipitation and dissolution of lithium metal forcharge/discharge reactions are considered to have great potentials. Thisis because they achieve energy densities higher than that achieved bylead batteries or nickel-cadmium batteries.

A secondary battery includes a positive electrode, a negative electrode,and an electrolyte. The positive electrode includes a positive electrodecollector and a positive electrode active material layer on the positiveelectrode collector. The negative electrode includes a negativeelectrode collector and a negative electrode active material layer onthe negative electrode collector. The electrolyte contains a solvent andan electrolyte salt.

The electrolyte functions as a medium for charge/discharge reactions andgreatly affects the performance of secondary batteries. Thus, variousinvestigations have been conducted on the composition of theelectrolyte.

In particular, in order to improve cycle characteristics and the like,formic acid, acetic acid, oxalic acid, malonic acid, maleic acid,fumaric acid, benzoic acid, and the like are used (e.g., refer toJapanese Unexamined Patent Application Publication Nos. 2000-012079 and2006-351242). Note that oxalic acid, succinic acid, malonic acid, adipicacid, sebacic acid, and phosphoric acid and their metal salts are alsoused in positive and negative electrodes as well as the electrolyte(e.g., refer to Japanese Unexamined Patent Application Publication Nos.09-190819, 09-190820, 2004-335379, 2005-011594, and 2006-134684). Inorder to improve cycle characteristics, storage characteristics, and thelike, disulfonic anhydrides, sulfonic-carboxylic anhydrides, etc., areused (e.g., refer to Japanese Unexamined Patent Application PublicationNos. 2004-022336 and 2002-008718)

SUMMARY

In recent years, portable electronic devices have shown increasinglyhigher performance and versatility and the power consumption of thesedevices tends to rise. Since charge/discharge operation of secondarybatteries is frequently repeated, cycle characteristics of the secondarybatteries tend to degrade easily. While portable electronic devices arecompact in size and can be carried along, they may be exposed to ahigh-temperature environment during transportation, storage, or thelike. Thus, storage characteristics of the secondary batteries also tendto degrade easily. In view of the above, further improvements in cyclecharacteristics and storage characteristics of the secondary batteriesare desired.

Thus, it is desirable to provide an electrolyte that can improve cyclecharacteristics and storage characteristics and a secondary battery thatuses such an electrolyte.

An electrolyte according to an embodiment of the present applicationincludes a solvent and an electrolyte salt. The solvent contains atleast one selected from ester compounds represented by formulae (1) to(3), lithium monofluorophosphate, and lithium difluorophosphate, and atleast one selected from anhydrous compounds represented by formulae (4)and (5) below. A secondary battery according to an embodiment of thepresent invention includes a positive electrode, a negative electrode,and an electrolyte that contains a solvent and an electrolyte salt, theelectrolyte having the above-described composition.

(R11 and R13 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof. R12represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof.)

(R14 and R16 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof. R15represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof.)

(R17 and R19 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof. R18represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof.)

(X21 represents a C2-C4 alkylene group that may be halogenated, a C2-C4alkenylene group that may be halogenated, an arylene group that may behalogenated, or a derivative thereof.)

(X22 represents a C2-C4 alkylene group that may be halogenated, a C2-C4alkenylene group that may be halogenated, an arylene group that may behalogenated, or a derivative thereof.).

Since the solvent in the electrolyte contains at least one selected fromester compounds represented by formulae (1) to (3), lithiummonofluorophosphate, and lithium difluorophosphate, and at least oneselected from anhydrous compounds represented by formulae (4) and (5),chemical stability of the electrolyte improves compared to when only oneor none of ester compound or the like and the anhydrous compound iscontained. Thus, when the electrolyte is used in a secondary battery,the cycle characteristics and the storage characteristics can beimproved

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view showing the structure of a firstsecondary battery including an electrolyte according to one embodiment;

FIG. 2 is an enlarged cross-sectional view of a part of a woundelectrode body shown in FIG. 1;

FIG. 3 is a schematic cross-sectional view showing the structure of anegative electrode shown in FIG. 2;

FIG. 4 is a schematic cross-sectional view showing another structure ofthe negative electrode shown in FIG. 2;

FIG. 5A is a scanning electron microscope (SEM) photograph showing across-sectional structure of the negative electrode shown in FIG. 2 andFIG. 5B is a schematic presentation of the SEM photograph shown in FIG.5A;

FIG. 6A is a SEM photograph showing another cross-sectional structure ofthe negative electrode shown in FIG. 2 and FIG. 6B is a schematicpresentation of the SEM photograph shown in FIG. 6A;

FIG. 7 is an exploded perspective view of a third secondary batteryincluding an electrolyte according to an embodiment;

FIG. 8 is a cross-sectional view of a wound electrode body shown in FIG.7 taken along line VIII-VIII; and

FIG. 9 is a graph showing results of analyzing a SnCoC-containingmaterial by X-ray photoelectron spectroscopy (XPS).

DETAILED DESCRIPTION

The present application will be described in detail below with referenceto the drawings according to an embodiment. The description is providedin the following order:

1. Electrolyte

2. Electrochemical devices (secondary batteries) using the electrolyte

2-1. First secondary battery (lithium ion secondary battery:cylindrical)

2-2. Second secondary battery (lithium metal secondary battery:cylindrical)

2-3. Third secondary battery (lithium ion secondary battery: laminatefilm)

1. Electrolyte

An electrolyte according to an embodiment is used in, for example,electrochemical devices such as secondary batteries and prepared bydissolving an electrolyte salt in a solvent. The electrolyte may containother materials such as various additives in addition to the solvent andthe electrolyte salt.

Solvent

The solvent contains at least one selected from ester compoundsrepresented by formulae (1) to (3) below, lithium monofluorophosphate,and lithium difluorophosphate, and at least one selected from anhydrouscompounds represented by formulae (4) and (5). This is because thechemical stability of the electrolyte is higher than when the solventcontains neither the ester compound or the like nor the anhydrouscompound or when the solvent contains only one of the ester compound orthe like and the anhydrous compound. In the description below, the estercompounds represented by formulae (1) to (3) are collectively referredto as “ester compound(s)” if desired and the anhydrous compoundsrepresented by formulae (4) and (5) are collectively referred to as“anhydrous compound(s)” if desired.

(R11 and R13 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof. R12represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof.)

(R14 and R16 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof. R15represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof.)

(R17 and R19 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof. R18represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof.)

(X21 represents a C2-C4 alkylene group that may be halogenated, a C2-C4alkenylene group that may be halogenated, an arylene group that may behalogenated, or a derivative thereof.)

(X22 represents a C2-C4 alkylene group that may be halogenated, a C2-C4alkenylene group that may be halogenated, an arylene group that may behalogenated, or a derivative thereof.)

The ester compound represented by formula (1) is a compound having estermoieties (—O—C(═O)—O—R) at both ends. R11 and R13 may be the same as ordifferent from each other.

For R11 and R13, examples of the alkyl group include the followinggroups: a methyl group, an ethyl group, a n (normal)-propyl group, anisopropyl group, a n-butyl group, an isobutyl group, a secondary (sec-)butyl group, a tertiary (tert-) butyl group, a n-pentyl group, a2-methylbutyl group, a 3-methylbutyl group, a 2,2-dimethylpropyl group,and a n-hexyl group. Examples of the alkenyl group include a n-heptylgroup, a vinyl group, a 2-methylvinyl group, a 2,2-dimethylvinyl group,a butene-2,4-diyl group, and an allyl group. An example of the alkynylgroup is an ethynyl group. The number of carbon atoms in the alkyl groupetc., described above is not particularly limited but is preferably 1 to20, more preferably 1 to 7, and most preferably 1 to 4. This is becausegood solubility and compatibility can be achieved.

When R11 and R13 are each an alkyl group or the like substituted with anaromatic hydrocarbon group or an alicyclic hydrocarbon group, thearomatic hydrocarbon group may be, for example, a phenyl group and thealicyclic hydrocarbon group may be, for example, a cyclohexyl group. Aphenyl-substituted alkyl group (aralkyl group) is, for example, a benzylgroup or a 2-phenylethyl group (phenetyl group).

When R11 and R13 are each a halogenated alkyl group or the like, forexample, the halogenated alkyl group may be a fluorinated alkyl group.Examples of the fluorinated alkyl group include a fluoromethyl group, adifluoromethyl group, a trifluoromethyl group, a 2,2,2-trifluoroethylgroup, and a pentafluoroethyl group. Note that a “halogenated group” isa group such as an alkyl group having at least part of hydrogen atomssubstituted with halogen.

In particular, R11 and R13 are each preferably a group substituted withan aromatic hydrocarbon group or an alicyclic hydrocarbon group ratherthan a halogenated group, and are each more preferably a group that isnot substituted with an aromatic hydrocarbon group or an alicyclichydrocarbon group. The number of carbon atoms in the group substitutedwith the aromatic hydrocarbon group or the alicyclic hydrocarbon groupis not particularly limited. The total number of carbon atoms in thearomatic or alicyclic hydrocarbon group and the alkyl group or the likeis preferably 20 or less and more preferably 7 or less. Note that R11and R13 may each be a derivative of an alkyl group or the like. Here, a“derivative” refers to a group, such as an alkyl group, into which oneor more substituents are introduced. The substituent may be ahydrocarbon group or any other group.

When R12 is a linear or branched alkylene group or the like, the numberof carbon atoms is not particularly limited but is preferably 2 to 10,more preferably 2 to 6, and most preferably 2 to 4. This is because goodsolubility and compatibility can be achieved. The divalent groupcontaining an arylene group and an alkylene group may be a group inwhich one arylene group is bonded to one alkylene group or a group(aralkylene) in which two alkylene groups are bonded through an arylenegroup.

In such a case, examples of R12 include following groups: linearalkylene groups represented by formulae (1-11) to (1-17), branchedalkylene groups represented by formulae (1-18) to (1-26), arylene groupsrepresented by formulae (1-27) to (1-29) and divalent groups representedby formulae (1-30) to (1-32) containing an arylene group and alkylenegroups. The divalent groups represented by formulae (1-30) to (1-32) areso-called benzylidene groups.

When R12 is a C2-C12 divalent group having an ether bond and an alkylenegroup, the divalent group is preferably a group having at least twoalkylene groups linked through an ether bond and carbon atoms at bothends. The number of carbon atoms of such a group is preferably 4 to 12.This is because good solubility and compatibility can be achieved. Itshould be noted that in the C2-C12 divalent group containing an etherbond and alkylene groups, the number of ether bonds and the order inwhich the ether bonds and the alkylene groups are linked can be freelyset.

Examples of R12 in such a case include groups represented by formulae(1-33) to (1-45). When the divalent groups represented by formulae(1-33) to (1-45) are fluorinated, examples of R12 include groupsrepresented by formulae (1-46) to (1-54). Among these, groupsrepresented by (1-38) to (1-40) are preferable. Note that R12 may be aderivative of the alkylene group or the like.

The molecular weight of the ester compound represented by formula (1) isnot particularly limited but is preferably 200 to 800, more preferably200 to 600, and most preferably 200 to 450. This is because goodsolubility and compatibility can be achieved.

Specific examples of the ester compound represented by formula (1)include a compound represented by formula (1-1). This is because higheffects can be achieved. The ester compound represented by formula (1)is not limited to one represented by formula (1-1) and may be any othercompound.

The ester compound represented by formula (2) is a compound having estermoieties (—O—C(═O)—R) at both ends. R14 and R16 may be the same as ordifferent from each other. The details for R14 and R16 are the same asthose for R11 and R13 described above. The details for R15 are the sameas those for R12 described above.

The molecular weight of the ester compound represented by formula (2) isnot particularly limited but is preferably 162 to 1000, more preferably162 to 500, and most preferably 162 to 300. This is because goodsolubility and compatibility can be achieved.

Specific examples of the ester compound represented by formula (2)include a compound represented by formula (2-1). This is because higheffects can be achieved.

Other examples of the ester compound represented by formula (2) includediethylene glycol dipropionate, diethylene glycol dibutyrate,triethylene glycol diacetate, triethylene glycol dipropionate,triethylene glycol dibutyrate, tetraethylene glycol diacetate,tetraethylene glycol dipropionate, and tetraethylene glycol dibutyrate.The ester compound represented by formula (2) is not limited to onerepresented by formula (2-1) and may be any other compound.

The ester compound represented by formula (3) is a compound having estermoieties (—O—S(═O)₂—R) at both ends. R17 and R19 may be the same as ordifferent from each other. The details for R17 and R19 are the same asthose for R11 and R13 described above. The details for R18 are the sameas those for R12 described above.

The molecular weight of the ester compound represented by formula (3) isnot particularly limited but is preferably 200 to 800, more preferably200 to 600, and most preferably 200 to 450. This is because goodsolubility and compatibility can be achieved.

Specific examples of the ester compound represented by formula (3)include a compound represented by formula (3-1). This is because higheffects can be achieved. The ester compound represented by formula (3)is not limited to one represented by formula (3-1) and may be any othercompound.

The anhydrous compound represented by formula (4) is a cyclic compoundhaving a disulfonic anhydride group (—S(O═)₂—O—S(O═)₂—). X21 may belinear or branched. A perfluoro group is particularly preferred as the“halogenated group”. The type of halogen is not particularly limited butfluorine is preferred. This is because chemical stability of theanhydrous compound can be improved. Here, a “derivative” refers to agroup, such as an alkyl group, into which one or more substituents areintroduced. The substituent may be a hydrocarbon group or any othergroup.

The number of carbon atoms in X21 is 2 to 4 since good solubility andcompatibility can be obtained and the chemical stability of theanhydrous compound can be improved. To be more specific, if the numberof carbon atoms is 1, sufficient chemical stability may not be obtainedand if the number is 5 or more, sufficient solubility and compatibilitymay not be obtained.

Specific examples of the anhydrous compound represented by formula (4)include compounds represented by formulae (4-1) to (4-22). The anhydrouscompound include geometric isomers. Among these, groups represented by(4-1) and (4-2) are preferable. This is because they can achieve higheffects and are highly available. The anhydrous compound represented byformula (4) is not limited to those represented by formulae (4-1) to(4-22) and may be any other compound.

The anhydrous compound represented by formula (5) is a cyclic compoundhaving a sulfonic-carboxylic anhydride group (—S(O═)₂—O—C(═O)—). Thedetails of the structure of and the number of carbon atoms in X22 arethe same as those of X21 described above.

Specific examples of the anhydrous compound represented by formula (5)include compounds represented by formulae (5-1) to (5-20). The anhydrouscompound include geometric isomers. Among these, the compoundrepresented by formula (5-1) is preferred. This is because it canachieve high effects and is highly available. The anhydrous compoundrepresented by formula (5) is not limited to those represented byformulae (5-1) to (5-20) and may be any other compound.

The content of at least one of the ester compounds, lithiummonofluorophosphate, and lithium difluorophosphate in the solvent is notparticularly limited. In particular, the content is preferably 0.001 wt% to 10 wt % and more preferably 0.001 wt % to 1 wt %. The anhydrouscompound content in the solvent is not particularly limited but ispreferably 0.01 wt % to 1 wt %. This is because chemical stability ofthe electrolyte can be improved further.

The solvent preferably contains a phosphoric acid compound representedby formula (6) in addition to the ester compound or the like and theanhydrous compound described above. This is because chemical stabilityof the electrolyte can be improved further.

(R31 to R33 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof.)

The details of R31 to R33 are the same as those of R11 and R13 describedabove. The molecular weight of the phosphoric acid compound is notparticularly limited but is preferably 200 to 800, more preferably 200to 600, and most preferably 200 to 450. This is because good solubilityand compatibility can be achieved.

Examples of the phosphoric acid compound include one represented byformula (6-1). This is because it can achieve high effects and is highlyavailable. The phosphoric acid compound is not limited to onerepresented by formula (6-1) and may be any other compound.

The phosphoric acid compound content in the solvent is not particularlylimited but is preferably 0.001 wt % to 1 wt %. This is because highereffects can be obtained.

The solvent may contain other materials as long as it contains the estercompound or the like and the anhydrous compound described above and, ifoccasion demands, the phosphoric acid compound. Examples of othermaterials include one or more nonaqueous solvents such as organicsolvents described below. Note that nonaqueous solvents that correspondto the ester compound or the like, the anhydrous compound, and thephosphoric acid compound are excluded from the nonaqueous solventsdescribed below.

Examples of the nonaqueous solvent include ethylene carbonate, propylenecarbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate,ethyl methyl carbonate, methyl propyl carbonate, γ-butyrolactone,γ-valerolactone, 1,2-dimethoxyethane, tetrahydrofuran,2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane,4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, methyl acetate, ethylacetate, methyl propionate, ethyl propionate, methyl butyrate, methylisobutyrate, methyl trim ethyl acetate, ethyl trimethyl acetate,acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile,3-methoxypropionitrile, N,N-dimethylformamide, N-methylpyrrolidinone,N-methyloxazolidinone, N,N′-dimethylimidazolidinone, nitromethane,nitroethane, sulfolane, trimethyl phosphate, and dimethyl sulfoxide.This is because electrochemical devices that use such electrolytesexhibit good characteristics. Examples of the characteristics includebattery capacities, cycle characteristics, and storage characteristicswhen electrolytes are used in secondary batteries.

Of these, at least one selected from ethylene carbonate, propylenecarbonate, dimethyl carbonate, diethyl carbonate, and ethyl methylcarbonate is preferred. This is because good battery capacities, cyclecharacteristics, storage characteristics, etc., can be obtained. In sucha case, a combination of a high-viscosity (high-dielectric-constant)solvent (e.g., relative dielectric constant ∈≧30) such as ethylenecarbonate or propylene carbonate and a low-viscosity solvent (e.g.,viscosity ≦1 mPa·s) such as dimethyl carbonate, ethyl methyl carbonate,or diethyl carbonate is more preferred. This is because thedissociability of the electrolyte salt and the mobility of ions improve.

In particular, the solvent preferably contains at least one selectedfrom unsaturated carbon bond-containing cyclic carbonic acid estersrepresented by formulae (7) to (9). This is because decompositionreaction of the electrolyte is suppressed by the formation of a stableprotective film on the electrode surface at the time of electrodereaction. The “unsaturated carbon bond-containing cyclic carbonic acidester” is a cyclic carbonic acid ester having an unsaturated carbonbond. The unsaturated carbon bond-containing cyclic carbonic acid estercontent in the solvent is, for example, 0.01 wt % to 10 wt %. The typeof the unsaturated carbon bond-containing carbonic acid ester is notlimited to those described below and may be any other type.

(R41 and R42 each represent a hydrogen group or an alkyl group.)

(R43 to R46 each represent a hydrogen group, an alkyl group, a vinylgroup, or an allyl group and at least one of R43 to R46 is a vinyl groupor an allyl group.)

(R47 represents an alkylene group.)

The unsaturated carbon bond-containing cyclic carbonic acid esterrepresented by formula (7) is a vinylene carbonate compound. Examples ofthe vinylene carbonate compound include vinylene carbonate, methylvinylene carbonate, ethyl vinylene carbonate,4,5-dimethyl-1,3-dioxol-2-one, 4,5-diethyl-1,3-dioxol-2-one,4-fluoro-1,3-dioxol-2-one, and 4-trifluoromethyl-1,3-dioxol-2-one. Ofthese, vinylene carbonate is preferred. This is because it is highlyavailable and achieves high effects.

The unsaturated carbon bond-containing cyclic carbonic acid esterrepresented by formula (8) is a vinyl ethylene carbonate compound.Examples of the vinyl ethylene carbonate compound include vinyl ethylenecarbonate, 4-methyl-4-vinyl-1,3-dioxolan-2-one,4-ethyl-4-vinyl-1,3-dioxolan-2-one,4-n-propyl-4-vinyl-1,3-dioxolan-2-one,5-methyl-4-vinyl-1,3-dioxolan-2-one, 4,4-divinyl-1,3-dioxolan-2-one, and4,5-divinyl-1,3-dioxolan-2-one. Of these, vinyl ethylene carbonate ispreferred. This is because it is highly available and achieves higheffects. Naturally, R23 to R26 may all be vinyl groups or allyl groupsor vinyl groups and allyl groups may be mixed.

The unsaturated carbon bond-containing cyclic carbonic acid esterrepresented by formula (9) is a methylene ethylene carbonate compound.Examples of the methylene ethylene carbonate compound include4-methylene-1,3-dioxolan-2-one,4,4-dimethyl-5-methylene-1,3-dioxolan-2-one, and4,4-diethyl-5-methylene-1,3-dioxolan-2-one. The methylene ethylenecarbonate compound may be a compound containing one methylene group(compound represented by formula (9)) or two methylene groups.

The unsaturated carbon bond-containing cyclic carbonic acid ester may bea catechol carbonate having a benzene ring or the like other than thecompounds represented by formulae (7) to (9).

The solvent preferably contains at least one selected from a halogenatedchain carbonic acid ester represented by formula (10) and a halogenatedcyclic carbonic acid ester represented by formula (11). This is becausedecomposition reaction of the electrolyte is suppressed by the formationof a stable protective film on the electrode surface at the time ofelectrode reaction. The “halogenated chain carbonic acid ester” is achain carbonic acid ester containing a halogen as a constitutionalelement. The “halogenated cyclic carbonic acid ester” is a cycliccarbonic acid ester containing a halogen as a constitutional element.R51 to R56 in formula (10) may be the same as or different from eachother. The same applies to R57 to R60 in formula (11). The total contentof the halogenated chain carbonic acid ester and the halogenated cycliccarbonic acid ester in the solvent is, for example, 0.01 wt % to 50 wt%. Note that the types of the halogenated chain carbonic acid ester andthe halogenated cyclic carbonic acid ester are not limited to thosedescribed below and may be any other types.

(R51 to R56 each represent a hydrogen group, a halogen group, an alkylgroup, or a halogenated alkyl group and at least one of R51 to R56 is ahalogen group or a halogenated alkyl group.)

(R57 to R60 each represent a hydrogen group, a halogen group, an alkylgroup, or a halogenated alkyl group and at least one of R57 to R60 is ahalogen group or a halogenated alkyl group.)

The type of halogen is not particularly limited but is preferablyfluorine, chlorine, or bromine. Fluorine is more preferred. This isbecause higher effects can be obtained compared to other halogens. Thenumber of halogen atoms is preferably 2 rather than 1 and may be 3 ormore. This is because the ability to form a protective film increasesand a stronger and more stable protective film is formed, resulting inhigher suppression of decomposition reaction of the electrolyte.

Examples of the halogenated chain carbonic acid ester includefluoromethyl methyl carbonate, bis(fluoromethyl) carbonate, anddifluoromethyl methyl carbonate. Examples of the halogenated cycliccarbonic acid ester include those represented by formulae (11-1) to(11-21). The halogenated cyclic carbonic acid esters include geometricisomers. Of these, 4-fluoro-1,3-dioxolan-2-one represented by formula(11-1) and 4,5-difluoro-1,3-dioxolan-2-one represented by formula (11-3)are preferred and the latter is more preferred. As for4,5-difluoro-1,3-dioxolan-2-one, cis isomers are preferred over transisomers. This is because they are highly available and achieve higheffects.

The solvent preferably contains a sultone (cyclic sulfonic acid ester).This is because chemical stability of the electrolyte can be improvedfurther. Examples of the sultone include propane sultone and propenesultone. The sultone content in the solvent is, for example, 0.5 wt % to5 wt %. The type of sultone is not limited to those described above andmay be any other type.

The solvent preferably further contains an acid anhydride. This isbecause chemical stability of the electrolyte can be improved further.Examples of the acid anhydride include carboxylic anhydrides. Examplesof the carboxylic anhydrides include succinic anhydride, glutaricanhydride, and maleic anhydride. The acid anhydride content in thesolvent is, for example, 0.5 wt % to 5 wt %. The type of acid anhydrideis not limited to those described above and may be any other type.

Electrolyte Salt

The electrolyte salt contains, for example, at least one light metalsalt such as a lithium salt. The electrolyte salt may further contain,for example, salts other than salts of light metals.

Examples of the lithium salts include lithium hexafluorophosphate,lithium tetrafluoroborate, lithium perchlorate, lithiumhexafluoroarsenate, lithium tetraphenylborate (LiB(C₆H₅)₄), lithiummethanesulfonate (LiCH₃SO₃), lithium trifluoromethanesulfonate(LiCF₃SO₃), lithium tetrachloroaluminate (LiAlCl₄), dilithiumhexafluorosilicate (Li₂SiF₆), lithium chloride (LiCl), lithium bromide(LiBr), lithium monofluorophosphate (Li₂PFO₃), and lithiumdifluorophosphate (LiPF₂O₂). This is because electrochemical devicesthat use such electrolytes exhibit good characteristics. The type ofelectrolyte salt is not limited to those described above and may be anyother type.

Of these, at least one selected from lithium hexafluorophosphate,lithium tetrafluoroborate, lithium perchlorate, and lithiumhexafluoroarsenate is preferred and lithium hexafluorophosphate is morepreferred. This is because the internal resistance decreases and highereffects are achieved.

In particular, the electrolyte salt preferably contains at least oneselected from the compounds represented by formulae (12) to (14). Thisis because higher effects can be obtained. R61 and R63 in formula (12)may be the same as or different from each other. The same applies to R71to R73 in formula (13) and R81 and R82 in formula (14). The type ofelectrolyte salt is not limited to those described below and may be anyother type.

(X61 represents a group 1A or 2A element in the short-form periodictable or aluminum. M61 represents a transition metal or a group 3B, 4B,or 5B element in the short-form periodic table. R61 represents a halogengroup. Y61 represents —C(═O)—R62-C(═O)—, —C(═O)—CR63₂-, or—C(═O)—C(═O)—, where R62 represents an alkylene group, a halogenatedalkylene group, an arylene group, or a halogenated arylene group, R63represents an alkyl group, a halogenated alkyl group, an aryl group, ora halogenated aryl group, a6 represents an integer of 1 to 4, b6represents an integer of 0, 2, or 4, and c6, d6, m6, and n6 eachrepresent an integer of 1 to 3.)

(X71 represents a group 1A or 2A element in the short-form periodictable. M71 represents a transition metal or a group 3B, 4B, or 5Belement in the short-form periodic table. Y71 represents—C(═O)—(CR71₂)_(b7)-C(═O)—, —R73₂C—(CR72₂)_(c7)-C(═O)—,—R73₂C—(CR72₂)_(c7)-CR73₂-, —R73₂C—(CR72₂)_(c7)-S(═O)₂—,—S(═O)₂—(CR72₂)_(d7)-S(═O)₂—, or —C(═O)—(CR72₂)_(d7)-S(═O)₂— where R71and R73 each represent a hydrogen group, an alkyl group, a halogengroup, or a halogenated alkyl group and at least one of R71 and R73 is ahalogen group or a halogenated alkyl group, R72 represents a hydrogengroup, an alkyl group, a halogen group, or a halogenated alkyl group,a7, e7, and n7 each represent an integer of 1 or 2, b7 and d7 eachrepresent an integer of 1 to 4, c7 represents an integer of 0 to 4, andf7 and m7 each represent an integer of 1 to 3.)

(X81 represents a group 1A or 2A element in the short-form periodictable. M81 represents a transition metal or a group 3B, 4B, or 5Belement in the short-form periodic table. Rf represents a C1-C10fluorinated alkyl group or a C1-C10 fluorinated aryl group. Y81represents —C(═O)—(CR81₂)_(d8)-C(═O)—, —R82₂C—(CR81₂)_(d8)-C(═O)—,—R82₂C—(CR81₂)_(d8)-CR82₂-, —R82₂C—(CR81₂)_(d8)-S(═O)₂—,—S(═O)₂—(CR81₂)_(e8)-S(═O)₂—, or —C(═O)—(CR81₂)_(e8)-S(═O)₂— where R81represents a hydrogen group, an alkyl group, a halogen group, or ahalogenated alkyl group, R82 represents a hydrogen group, an alkylgroup, a halogen group, or a halogenated alkyl group and at least one ofR82s is a halogen group or a halogenated alkyl group, a8, f8, and n8each represent an integer of 1 or 2, b8, c8, and e8 each represent aninteger of 1 to 4, d8 represents an integer of 0 to 4, and g8 and m8each represent an integer of 1 to 3.)

Examples of the group 1A element include hydrogen, lithium, sodium,potassium, rubidium, cesium, and francium. Examples of the group 2Aelement include beryllium, magnesium, calcium, strontium, barium, andradium. Examples of the group 3B element include boron, aluminum,gallium, indium, and thallium. Examples of the group 4B element includecarbon, silicon, germanium, tin, and lead. Examples of the group 5Belement include nitrogen, phosphorus, arsenic, antimony, and bismuth.

Examples of the compound represented by formula (12) include compoundsrepresented by formulae (12-1) to (12-6). Examples of the compoundrepresented by formula (13) include compounds represented by formulae(13-1) to (13-8). Examples of the compound represented by formula (14)include a compound represented by formula (14-1).

The electrolyte salt preferably contains at least one selected from thecompounds represented by formulae (15) to (17). This is because highereffects can be obtained. Note that m and n in formula (15) may representthe same value or different values. The same applies to p, q, and r informula (17). The type of electrolyte salt is not limited to thosedescribed below and may be any other.LiN(C_(m)F_(2m+1)SO₂)(C_(n)F_(2n+1)SO₂)  (15)(m and n each represent an integer of 1 or more.)

(R91 represents a C2-C4 linear or branched perfluoroalkylene group.)LiC(C_(p)F_(2p+1)SO₂)(C_(q)F_(2q+1)SO₂)(C_(r)F_(2r+1)SO₂)  (17)(p, q, and r each represent an integer of 1 or more.)

The compound represented by formula (15) is a chain imide compound.Examples of this compound include lithiumbis(trifluoromethanesulfonyl)imide (LiN(CF₃SO₂)₂), lithiumbis(pentafluoroethanesulfonyl)imide (LiN(C₂F₅SO₂)₂), lithium(trifluoromethanesulfonyl)(pentafluoroethanesulfonyl)imide(LiN(CF₃SO₂)(C₂F₅SO₂)), lithium(trifluoromethanesulfonyl)(heptafluoropropanesulfonyl)imide(LiN(CF₃SO₂)(C₃F₇SO₂)), and lithium(trifluoromethanesulfonyl)(nonafluorobutanesulfonyl)imide(LiN(CF₃SO₂)(C₄F₉SO₂)).

The compound represented by formula (16) is a cyclic imide compound.Examples of this compound include those represented by formulae (16-1)to (16-4).

The compound represented by formula (17) is a chain methide compound. Anexample of this compound is lithiumtris(trifluoromethanesulfonyl)methide (LiC(CF₃SO₂)₃).

The electrolyte salt content is preferably 0.3 mol/kg to 3.0 mol/kg withrespect to the solvent. This is to achieve a high ion conductivity.

According to this electrolyte, the solvent contains at least oneselected from ester compounds, lithium monofluorophosphate, and lithiumdifluorophosphate, and at least one anhydrous compound. This improveschemical stability of the electrolyte compared to when the solventcontains neither the ester compound or the like nor the anhydrouscompound or when the solvent contains only one of the ester compound orthe like and the anhydrous compound. Accordingly, since decompositionreaction of the electrolyte at the time of electrode reactions issuppressed, performance of electrochemical devices that use theelectrolyte can be improved.

In particular, when the content of at least one selected from the estercompound, lithium monofluorophosphate, and lithium difluorophosphate is0.001 wt % to 10 wt % in the solvent, higher effects can be achieved.When the anhydrous compound content in the solvent is 0.01 wt % to 1 wt%, higher effects can be achieved.

When the solvent contains a phosphoric acid compound, higher effects canbe achieved.

Higher effects can be achieved when the solvent contains at least oneselected from an unsaturated carbon bond-containing cyclic carbonic acidester, a halogenated chain carbonic acid ester, a halogenated cycliccarbonic acid ester, a sultone, and an acid anhydride. Higher effectscan be achieved when the electrolyte salt contains at least one selectedfrom lithium hexafluorophosphate, lithium tetrafluoroborate, lithiumperchlorate, lithium hexafluoroarsenate, and compounds represented byformulae (12) to (17).

2. Electrochemical Devices (Secondary Batteries) Using the Electrolyte

Next, examples of using the electrolyte described above are described. Asecondary battery is used as an example of the electrochemical device.The electrolyte described above is used as follows.

2-1. First Secondary Battery

FIGS. 1 and 2 show cross-sectional structures of a first secondarybattery. FIG. 2 is an enlarged view of a part of a wound electrode body20 shown in FIG. 1. The secondary battery described herein is, forexample, a lithium ion secondary battery in which the capacity of thenegative electrode is indicated by occlusion and release of lithium ionsthat serve as an electrode reactant.

Overall Structure of the Secondary Battery

This secondary battery includes a substantially hollow-cylinder-shapedbattery can 11 containing the wound electrode body 20 and a pair ofisolators 12 and 13. A battery structure that uses such a battery can 11is called a cylindrical type.

The battery can 11 has, for example, a hollow structure having one endclosed and the other end open and is composed of iron, aluminum, analloy thereof, or the like. When the battery can 11 is composed of iron,the surface of the battery can 11 may be plated with nickel, forexample. The pair of isolators 12 and 13 sandwich the wound electrodebody 20 in a vertical direction and extend perpendicularly with respectto the wound peripheral surface of the wound electrode body 20.

A battery lid 14, a safety valve mechanism 15, and a thermosensitiveresistor (positive temperature coefficient (PCT) element) 16 are caulkedat the open end of the battery can 11 through a gasket 17 and thebattery can 11 is thereby sealed. The battery lid 14 is composed of thesame material as the battery can 11, for example. The safety valvemechanism 15 and the thermosensitive resistor 16 are provided at theinner side of the battery lid 14. The safety valve mechanism 15 iselectrically connected to the battery lid 14 through the thermosensitiveresistor 16. The safety valve mechanism 15 is configured such that whenthe internal pressure reaches a particular level or higher due tointernal shorts, heat from outside, etc., a disk 15A is reversed to cutthe electrical connection between the battery lid 14 and the woundelectrode body 20. The thermosensitive resistor 16 prevents abnormalheat generation caused by high current since its resistance increases(thereby restricting the current) with the increase in temperature. Thegasket 17 is composed of, for example, an insulating material and thesurface thereof is coated with, for example, asphalt.

The wound electrode body 20 includes a positive electrode 21 and anegative electrode 22 laminated with a separator 23 therebetween andwound. A center pin 24 may be inserted into the center of the woundelectrode body 20. In the wound electrode body 20, a positive electrodelead 25 composed of aluminum or the like is connected to the positiveelectrode 21, and a negative electrode lead 26 composed of nickel or thelike is connected to the negative electrode 22. The positive electrodelead 25 is electrically connected to the battery lid 14 by being weldedto the safety valve mechanism 15, for example. The negative electrodelead 26 is electrically connected to the battery can 11 by being weldedthereto, for example.

Positive Electrode

The positive electrode 21 includes, for example, a positive electrodecollector 21A and positive electrode active material layers 21B formedon both sides of the positive electrode collector 21A. Alternatively,the positive electrode active material layer 21B may be disposed on onlyone side of the positive electrode collector 21A.

The positive electrode collector 21A is composed of, for example,aluminum, nickel, or stainless steel.

The positive electrode active material layer 21B contains a positiveelectrode active material which is at least one positive electrodematerial that can occlude and release lithium ions. The positiveelectrode active material layer 21B may further contain other materialssuch as a positive electrode binder and a positive electrode conductantagent if necessary.

The positive electrode material is preferably a lithium-containingcompound since a high energy density can be achieved. Examples of thelithium-containing compound include a complex oxide containing lithiumand a transition metal element as constitutional elements and aphosphoric acid compound containing lithium and a transition metalelement as constitutional elements. In particular, a compound containingat least one selected from cobalt, nickel, manganese, and iron as thetransition metal element is preferred since a higher voltage can beobtained. The chemical formula therefor is, for example, Li_(x)M1O₂ orLi_(y)M2PO₄. In the formula, M1 and M2 each represent at least onetransition metal element. The values of x and y vary depending on thecharge/discharge state but are usually 0.05≦x≦1.10 and 0.05≦y≦1.10.

Examples of the complex oxide containing lithium and a transition metalelement include lithium-cobalt complex oxide (Li_(x)CoO₂),lithium-nickel complex oxide (Li_(x)NiO₂), and lithium-nickel complexoxides represented by formula (18). Examples of the phosphoric acidcompound containing lithium and a transition metal element includelithium-iron phosphoric acid compound (LiFePO₄) andlithium-iron-manganese phosphoric acid compound (LiFe_(1−u)Mn_(u)PO₄(u<1)). This is because good cycle characteristics can be obtained aswell as a high battery capacity.LiNi_(1−x)M_(x)O₂  (18)

(M is at least one selected from cobalt, manganese, iron, aluminum,vanadium, tin, magnesium, titanium, strontium, calcium, zirconium,molybdenum, technetium, ruthenium, tantalum, tungsten, rhenium,ytterbium, copper, zinc, barium, boron, chromium, silicon, gallium,phosphorus, antimony, and niobium. X satisfies 0.005<x<0.5.)

Other examples of the positive electrode material include oxides,disulfides, chalcogenides, and electrically conductive polymers.Examples of the oxides include titanium oxide, vanadium oxide, andmanganese dioxide. Examples of the disulfides include titanium disulfideand molybdenum sulfide. Examples of the chalcogenides include niobiumselenide. Examples of the electrically conductive polymers includesulfur, polyaniline, and polythiophene.

The positive electrode material may be any other material. A series ofpositive electrode materials described above may be used as a mixture ofany combination of two or more types.

Examples of the positive electrode binder include synthetic rubber suchas styrene-butadiene rubber, fluorine rubber, andethylene-propylene-diene and polymer materials such as polyvinylidenefluoride. These may be used alone or in combination.

Examples of the positive electrode conductant agent include carbonmaterials such as graphite, carbon black, acetylene black, and Ketjenblack. These may be used alone or in combination. The positive electrodeconductant agent may be a metal material or electrically conductivepolymer as long as the material has electrical conductivity.

Negative Electrode

The negative electrode 22 includes, for example, a negative electrodecollector 22A and negative electrode active material layers 22B formedon both sides of the negative electrode collector 22A. Alternatively,the negative electrode active material layer 22B may be disposed on onlyone side of the negative electrode collector 22A.

The negative electrode collector 22A is composed of, for example,copper, nickel, or stainless steel. The surface of the negativeelectrode collector 22A is preferably roughened. This is because aso-called “anchoring effect” helps improve adhesiveness of the negativeelectrode active material layers 22B to the negative electrode collector22A. In such a case, the surface of the negative electrode collector 22Amay be roughened at least in a region that opposes the negativeelectrode active material layer 22B. The method of roughening thesurface may be, for example, a method for forming fine particles by anelectrolytic process. The electrolytic process is a process of formingirregularities by forming fine particles on the surface of the negativeelectrode collector 22A by an electrolytic process in an electrolyticcell. A copper foil produced by an electrolytic process is generallycalled “electrolytic copper foil”.

The negative electrode active material layer 22B contains a negativeelectrode active material which is at least one negative electrodematerial that can occlude and release lithium ions. The negativeelectrode active material layer 22B may further contain other materialssuch as a negative electrode binder and a negative electrode conductantagent if necessary. The details of the negative electrode binder and thenegative electrode conductant agent are the same as those of thepositive electrode binder and the positive electrode conductant agent,respectively, for example. For this negative electrode active materiallayer 22B, for example, the chargeable capacity of the negativeelectrode material is preferably larger than the discharge capacity ofthe positive electrode 21 in order to prevent unintended precipitationof lithium metal during charge/discharge operation.

Examples of the negative electrode material include carbon materials.Carbon materials undergo significantly small changes in crystalstructure during occlusion and release of lithium ions and thus a highenergy density and good cycle characteristics can be obtained. Thecarbon materials also function as negative electrode conductant agents.Examples of the carbon material include graphitizable carbon,non-graphitizable carbon having a (002) plane spacing of 0.37 nm ormore, and graphite having a (002) plane spacing of 0.34 nm or less. Inparticular, pyrolytic carbons, cokes, glassy carbon fibers, organicpolymer compound sinters, activated carbon, and carbon blacks can benamed. Of these, cokes include pitch cokes, needle cokes, and petroleumcokes. The organic polymer compound sinters refer to phenol or furanresins carbonized by firing at a suitable temperature. The form of thecarbon material may be fibrous, spherical, granular, or scaly.

The negative electrode material may be a material (metal-based material)containing at least one selected from metal and semimetal elements as aconstitutional element. This is because a high energy density isachieved. This material may be a metal or semimetal element in the formof a single element, an alloy, or a compound, may contain two or more ofsuch metal and/or semimetal elements, or may at least partly include aphase containing one or more of such metal and/or semimetal elements.For the purpose of this specification, “alloy” refers to not only amaterial that contains two or more metal elements but also a materialthat contains at least one metal element and at least one semimetalelement. The “alloy” may also contain a non-metal element. The structurethereof may be a solid solution, a eutectic crystal (eutectic mixture),an intermetallic compound, or a combination of two or more of theforegoing.

The metal or semimetal element described above is a metal or semimetalelement that can be alloyed with lithium and that is at least oneselected from the following elements: magnesium, boron, aluminum,gallium, indium (In), silicon, germanium (Ge), tin, lead (Pb), bismuth(Bi), cadmium (Cd), silver (Ag), zinc, hafnium (Hf), zirconium, yttrium,palladium (Pd), and platinum (Pt). Among these, at least one of siliconand tin is preferred. This is because silicon and tin have superbcapacity to occlude and release lithium ions and help achieve a highenergy density.

A material containing at least one of silicon and tin may be silicon ortin in the form of a single element, an alloy, or a compound, maycontain two or more of such silicon and tin, or may at least partlyinclude a phase containing one or more of such silicon and tin.

Examples of the silicon alloy include those alloys that contain at leastone of the following elements as a constitutional element other thansilicon: tin, nickel, copper, iron, cobalt, manganese, zinc, indium,silver, titanium, germanium, bismuth, antimony, and chromium. Examplesof the silicon compound include compounds that contain oxygen and/orcarbon as a constitutional element other than silicon. The siliconcompound may contain, as a constitutional element other than silicon, atleast one of the elements described with reference to the silicon alloy.

Examples of the silicon alloy and the silicon compound include SiB₄,SiB₆, Mg₂Si, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu₅Si,FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄, Si₂N₂O,SiO_(v) (0<v≦2), SnO_(w) (0<w≦2), and LiSiO.

Examples of the tin alloy include those alloys that contain at least oneof the following elements as a constitutional element other than tin:silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver,titanium, germanium, bismuth, antimony, and chromium. Examples of thetin compound include compounds containing oxygen and/or carbon. The tincompound may contain, as a constitutional element other than tin, atleast one of the elements described with reference to the tin alloy.Examples of the tin alloy and the tin compound include SnSiO₃, LiSnO,and Mg₂Sn.

In particular, the material containing silicon is preferably silicon inthe form of a single element, for example, since a high battery capacityand good cycle characteristics can be obtained. Note that the term“single element” is used here in general context (trace amounts ofimpurities may be present) and does not always mean that the purity is100%.

The material containing tin is preferably a material that contains asecond constitutional element and a third constitutional element inaddition to tin as a first constitutional element, for example. Thesecond constitutional element is, for example, at least one selectedfrom the following elements: cobalt, iron, magnesium, titanium,vanadium, chromium, manganese, nickel, copper, zinc, gallium, zirconium,niobium, molybdenum, silver, indium, cerium (Ce), hafnium, tantalum,tungsten (W), bismuth, and silicon. The third constitutional element is,for example, at least one selected from boron, carbon, aluminum, andphosphorus. When the second and third constitutional elements arecontained, a high battery capacity and good cycle characteristics can beobtained.

In particular, a material containing tin, cobalt, and carbon(SnCoC-containing material) is preferable. As for the composition of theSnCoC-containing material, the carbon content is, for example, 9.9 mass% to 29.7 mass % and the ratio of the cobalt content to the totalcontent of tin and cobalt (Co/(Sn+Co)) is 20 mass % to 70 mass %. A highenergy density can be obtained within such a compositional range.

The SnCoC-containing material has a phase containing tin, cobalt, andcarbon. This phase preferably has a low crystallinity or is amorphous.This phase is a reactive phase that can react with lithium and presenceof the reactive phase helps achieve good characteristics. The half widthof the diffraction peak obtained by analyzing the phase by X-raydiffraction is preferably 1.0° or more in terms of a 2θ diffractionangle when a CuKα line is used as a characteristic X-ray at a sweep rateof 1°/min. This is because lithium ions can be occluded and releasedmore smoothly and the reactivity with the electrolyte and the likedecreases. Note that the SnCoC-containing material sometimes containsphases that contain the constitutional elements in the form of a singleelement or that contain some of the constitutional elements in additionto the low crystallinity or amorphous phase.

Whether or not the diffraction peak obtained by the X-ray diffractioncorresponds to the reactive phase that can react with lithium can beeasily determined by comparing the X-ray diffraction charts before andafter the electrochemical reaction with lithium. For example, if theposition of the diffraction peak changes between before and after theelectrochemical reaction with lithium, the peak corresponds to thereactive phase that can react with lithium. In such a case, for example,the diffraction peak of the low-crystallinity or amorphous reactivephase is observed at 2θ=20° to 50°. This reactive phase, for example,contains the constitutional elements described above and presumably hasa low crystallinity or is amorphous because of the presence of carbon.

In the SnCoC-containing material, at least part of atoms of carbonserving as a constitutional element are preferably bonded to anotherconstitutional element, i.e., a metal or semimetal element. This isbecause aggregation or crystallization of tin is suppressed. The stateof bonding between elements can be confirmed through X-ray photoelectronspectroscopy (XPS), for example. In a commercially available device, anAl—Kα line, a Mg—Kα line, or the like is used as a soft X-ray, forexample. When at least part of atoms of carbon are bonded with a metalor semimetal element or the like, the peak of the composite wave of thecarbon is orbital (C is) appears in a region lower than 284.5 eV. Itshould be noted that the energy calibration has been set so that thepeak of the 4f orbital of gold atoms (Au4f) appears at 84.0 eV. Duringthis operation, since surface-contaminating carbon is usually present ona surface of a material, the C1s peak of the surface-contaminatingcarbon is set at 284.8 eV and used as the energy reference. In XPSanalysis, the waveform of the C1s peak is obtained as a combination ofthe peak of the surface-contaminating carbon and the peak of carboncontained in the SnCoC-containing material. Thus, the two peaks areseparated by analysis using commercially available software, forexample. In the waveform analysis, the position of the main peak at thelowest binding energy side is used as the energy reference (284.8 eV).

The SnCoC-containing material may include other constitutional elementsif necessary. At least one element selected from silicon, iron, nickel,chromium, indium, niobium, germanium, titanium, molybdenum, aluminum,phosphorus, gallium, and bismuth is an example of such constitutionalelements.

In addition to the SnCoC-containing material, a material containing tin,cobalt, iron, and carbon (SnCoFeC-containing material) is alsopreferable. The composition of the SnCoFeC-containing material may befreely set. For example, the following composition can be employed whenthe iron content is to be set low: 9.9 mass % to 29.7 mass % carbon and0.3 mass % to 5.9 mass % iron with the ratio of cobalt content to thetotal content of tin and cobalt (Co/(Sn+Co)) being 30 mass % to 70 mass%. For example, the following composition can be employed when the ironcontent is to be set high: 11.9 mass % to 29.7 mass % carbon with theratio of the total content of iron and cobalt to the total content oftin, cobalt, and iron ((Co+Fe)/(Sn+Co+Fe)) being 26.4 mass % to 48.5mass % and the ratio of the cobalt content to the total content ofcobalt and iron (Co/(Co+Fe)) being 9.9 mass % to 79.5 mass %. A highenergy density can be obtained within such compositional ranges. Thephysical properties (such as the half width) of the SnCoFeC-containingmaterial are the same as those of the SnCoC-containing materialdescribed above.

Examples of other negative electrode material include metal oxides andpolymer compounds. Examples of the metal oxides include iron oxide,ruthenium oxide, and molybdenum oxide. Examples of the polymer compoundinclude polyacetylene, polyaniline, and polypyrrole.

Naturally, the negative electrode material may be any other materials. Aseries of negative electrode active materials described above may beused as a mixture of any two or more types.

The negative electrode active material layers 22B are formed by, forexample, any one of an application method, a vapor phase method, aliquid phase method, a thermal spraying method, and a baking method(sintering method), or any combination of these method. The applicationmethod involves mixing a negative electrode active material in aparticle form with a binder and the like, dispersing the resultingmixture into a solvent, and applying the resulting dispersion. Examplesof the vapor phase method include a physical vapor deposition method anda chemical vapor deposition method. Specific examples thereof include avacuum vapor deposition method, a sputtering method, an ion platingmethod, a laser ablation method, a thermochemical vapor depositionmethod and a plasma-enhanced chemical vapor deposition method. Examplesof the liquid phase method include an electrolytic plating method and anelectroless plating method. The thermal spraying method involvesspraying a negative electrode active material in a molten or semi-moltenstate. The baking method involves, for example, performing applicationby the same process as the application method and then heating theapplied dispersion at a temperature higher than the melting temperatureof the binder or the like. A common technique can be employed for thebaking method. Examples thereof include an atmospheric baking method, areactive baking method, and a hot-press baking method.

The negative electrode active material is, for example, in the form ofparticles. In such a case, the negative electrode active material layer22B contains particles of a negative electrode active material (simplyreferred to as “negative electrode active material particles”hereinafter). When the negative electrode active material layer 22B isformed by an application method or the like, the negative electrodeactive material particles are the negative electrode active material ina particle form used for preparing a slurry for application. Incontrast, when the negative electrode active material layer 22B isformed by a vapor phase method or a thermal spraying method, thenegative electrode active material particles are particles of thenegative electrode active material deposited on the negative electrodecollector 22A by evaporation or melting.

When the negative electrode active material particles are formed by adeposition method such as a vapor phase method, the negative electrodeactive material particles may have a single-layer structure formed by asingle deposition process or a multilayer structure formed by conductinga deposition process a plurality of times. However, when an evaporationmethod that involves high-temperatures during deposition is used, thenegative electrode active material particles preferably have amultilayer structure. This is because the time for which the negativeelectrode collector 22A is exposed to high temperatures is shorter whenthe deposition of the negative electrode material is conducted over aplurality of times (the thickness of the negative electrode materialdeposited each time is smaller) than when the deposition is conducted inone step. As a result, the negative electrode collector 22A is lesslikely to be damaged by heat.

The negative electrode active material particles grow in the thicknessdirection of the negative electrode active material layer 22B from thesurface of the negative electrode collector 22A and are preferablyconnected to the negative electrode collector 22A at their bases. Thisis because expansion and contraction of the negative electrode activematerial layer 22B are suppressed during charge/discharge operation. Thenegative electrode active material particles are preferably formed by avapor phase method, a liquid phase method, a baking method, or the likeand are preferably alloyed with at least part of the interface with thenegative electrode collector 22A. In this case, the constitutionalelements of the negative electrode collector 22A may be diffused intothe negative electrode active material particles, the constitutionalelements of the negative electrode active material particles may bediffused into the negative electrode collector 22A, or theconstitutional elements of the negative electrode collector 22A and thenegative electrode active material particles may be interdiffused at theinterface.

In particular, the negative electrode active material layer 22Bpreferably includes an oxide-containing film coating the surfaces of thenegative electrode active material particles (the portions of thenegative electrode active material particles that come into contact withthe electrolyte if not for the oxide-containing film), if occasiondemands. This is because the oxide-containing film serves as aprotective film against the electrolyte and the decomposition reactionof the electrolyte can be suppressed during charge/discharge operation.As a result, the cycle characteristics, the storage characteristics, andthe like improve. The oxide-containing film may coat the entire surfacesor part of the surfaces of the negative electrode active materialparticles. Preferably, the entire surfaces are coated. This is becausethe decomposition reaction of the electrolyte can be suppressed further.

The oxide-containing film contains, for example, at least one selectedfrom a silicon oxide, a germanium oxide, and a tin oxide and preferablycontains a silicon oxide. This is because it becomes easier to coat theentire surfaces of the negative electrode active material particles andgood protection can be achieved. Naturally, the oxide-containing filmmay contain any other oxide.

The oxide-containing film is formed by, for example, a vapor phasemethod or a liquid phase method but is preferably formed by a liquidphase method. This is because it becomes easier to coat a wide range ofthe negative electrode active material particle surfaces. Examples ofthe liquid phase method include a liquid phase precipitation method, asol-gel method, an application method and a dip-coating method. Ofthese, the liquid phase precipitation method, the sol-gel method, andthe dip-coating method are preferred, and the liquid phase precipitationmethod is more preferred. This is because higher effects can beobtained. The oxide-containing film may be formed by one or more formingmethods among a series of forming methods described above.

If occasion demands, the negative electrode active material layer 22Bpreferably contains a metal material containing as a constitutionalelement a metal element that does not alloy with lithium, the metalmaterial occupying voids inside the negative electrode active materiallayer 22B (hereinafter this metal material is simply referred to as“metal material”). This is because the negative electrode activematerial particles become bonded to each other through the metalmaterial, the void ratio in the negative electrode active material layer22B decreases, and thus expansion and contraction of the negativeelectrode active material layer 22B are suppressed. As a result, thecycle characteristics, the storage characteristics, and the likeimprove. Note that the details of the “voids inside the negativeelectrode active material layer 22B” are described below (refer to FIGS.5A to 6B).

The metal element is, for example, at least one selected from the groupconsisting of iron, cobalt, nickel, zinc, and copper and is preferablycobalt. This is because the metal material can easily enter the voidsinside the negative electrode active material layer 22B and exhibits agood bonding effect. Naturally, the metal element may be any other metalelement. For the purpose of this specification, the term “metalmaterial” is not limited to a single element and represents a wideconcept including alloys and metal compounds.

The metal material is formed by, for example, a vapor phase method or aliquid phase method but is preferably formed by a liquid phase method.This is because the metal material can easily enter the voids inside thenegative electrode active material layer 22B. The liquid phase methodmay be an electrolytic plating method or an electroless plating methodbut is preferably an electrolytic plating method. This is because it iseasier for the metal material to enter the voids and the time taken forthe fabrication can be made shorter. The metal material may be formed byemploying one or more forming methods among a series of forming methodsdescribed above.

The negative electrode active material layer 22B may include one or bothof the oxide-containing film and the metal material. Preferably, bothare included to improve the cycle characteristics and the like. If onlyone of them is to be included, the oxide-containing film is preferablyincluded to improve the cycle characteristics and the like. When boththe oxide-containing film and the metal material are included, eitherone may be formed first. Preferably, the oxide-containing film is formedfirst to further improve the cycle characteristics and the like.

The detailed structure of the negative electrode 22 will now bedescribed with reference to FIGS. 3 to 6B.

First, the case in which the negative electrode active material layer22B includes negative electrode active material particles and anoxide-containing film is described. FIGS. 3 and 4 are schematic diagramsshowing cross-sectional structures of the negative electrode 22. Thedrawings show the case in which the negative electrode active materialparticles have a single-layer structure.

In the case shown in FIG. 3, negative electrode active materialparticles 221 are formed on the negative electrode collector 22A bydepositing a negative electrode material on the negative electrodecollector 22A by, for example, a vapor phase method such as a vapordeposition method. In this case, when the surface of the negativeelectrode collector 22A is roughened and has protrusions (e.g., fineparticles formed by an electrolytic process), the negative electrodeactive material particles 221 grow in the thickness direction for everyprotrusion. Thus, the negative electrode active material particles 221align on the negative electrode collector 22A and the bases thereof arebonded to the negative electrode collector 22A. When an oxide-containingfilm 222 is subsequently formed on the surfaces of the negativeelectrode active material particles 221 by, for example, a liquid phasemethod such as a liquid phase precipitation method, the oxide-containingfilm 222 coats substantially the entire surfaces of the negativeelectrode active material particles 221. In this case, a wide rangeextending from the top to the bottom of the negative electrode activematerial particles 221 can be coated. Such a wide-range coating state isa feature achieved when the oxide-containing film 222 is formed by aliquid phase method. In other words, when the oxide-containing film 222is formed by a liquid phase method, the coating effect reaches not onlythe top of the negative electrode active material particles 221 but alsothe bases of the negative electrode active material particles 221 sothat even the bases are coated with the oxide-containing film 222.

In contrast, in the case shown in FIG. 4, only part (top) of thenegative electrode active material particles 221 is coated with anoxide-containing film 223 since the oxide-containing film 223 is formedby a vapor phase method after the negative electrode active materialparticles 221 are formed by a vapor phase method. Such a narrowly coatedstate is a feature achieved when the oxide-containing film 223 is formedby a vapor phase method. In other words, when the oxide-containing film223 is formed by a vapor phase method, the coating effect reaches thetop of the negative electrode active material particles 221 but not thebase, and the bases remain uncoated with the oxide-containing film 223.

Although FIG. 3 illustrates the cases in which the negative electrodeactive material layer 22B is formed by a vapor phase method, the sameresult can be obtained when the negative electrode active material layer22B is formed by other methods such as an application method or a bakingmethod. That is, the oxide-containing film 222 coating substantially theentire surfaces of the negative electrode active material particles isformed.

Next, the case in which the negative electrode active material layer 22Bincludes negative electrode active material particles and a metalmaterial is described. FIGS. 5A, 5B, 6A, and 6B are enlarged views ofcross-sectional structures of the negative electrode 22. FIGS. 5A and 6Aare each a photograph (secondary electron image) taken with a scanningelectron microscope (SEM) and FIGS. 5B and 6B are each a schematicpresentation of the SEM photograph shown in FIG. 5A or 6A. The drawingsshow the case in which the negative electrode active material particles221 have a multilayer structure.

As shown in FIGS. 5A and 5B, when the negative electrode active materialparticles 221 have a multilayer structure, a plurality of voids 224 aregenerated inside the negative electrode active material layer 22B due tothe alignment structure, the multilayer structure, and the surfacestructure of the particles. The voids 224 include mainly two types ofvoids 224A and 224B classified according to the cause of generation. Thevoids 224A are generated between the negative electrode active materialparticles 221 and the voids 224B are generated between layers in thenegative electrode active material particles 221. Other types of voids224 generated by other causes may also be present.

In some cases, gaps 225 are generated in exposed surfaces (outermostsurfaces) of the negative electrode active material particles 221. Suchgaps 225 are generated between whisker-like fine projections (not shown)generated on the surfaces of the negative electrode active materialparticles 221. The gaps 225 may be generated across the exposed surfacesof the negative electrode active material particles 221 in some casesand only partially in other cases. Since the whisker-like projectionsoccur on the surfaces of the negative electrode active materialparticles 221 each time formation of the negative electrode activematerial particles 221 is conducted, the gaps 225 sometimes occur notonly on the exposed surfaces of the negative electrode active materialparticles 221 but also between the layers.

As shown in FIGS. 6A and 6B, the negative electrode active materiallayer 22B includes a metal material 226 in the voids 224A and 224B. Inthis case, the metal material 226 may be contained in one of the voids224A and 224B but is preferably contained in both the voids 224A and224B. This is because higher effects can be obtained.

The metal material 226 is in the voids 224A between the negativeelectrode active material particles 221. In particular, when thenegative electrode active material particles 221 are formed by a vaporphase method or the like, the negative electrode active materialparticles 221 grow for every protrusion present on the surface of thenegative electrode collector 22A, as mentioned earlier. Thus, the voids224A are generated between the negative electrode active materialparticles 221. The voids 224A cause the bonding property of the negativeelectrode active material layer 22B to decrease. Thus, in order toenhance the bonding property, the voids 224A are filled with the metalmaterial 226. In this case, it is sufficient if just part of the voids224A is filled but the amount of the voids 224A filled is preferably aslarge as possible. This is to enhance the bonding property of thenegative electrode active material layer 22B. The proportion of thevoids filled with the metal material 226 (filling percentage) ispreferably 20% or more, more preferably 40% or more, and most preferably80% or more.

The metal material 226 also enters the voids 224B inside the negativeelectrode active material particles 221. To be more specific, when thenegative electrode active material particles 221 have a multilayerstructure, the voids 224B are generated between the layers. As with thevoids 224A, the voids 224B also cause the bonding property of thenegative electrode active material layer 22B to decrease. Thus, in orderto enhance the bonding property, the voids 224B are filled with themetal material 226. In this case, it is sufficient if just part of thevoids 224B is filled but the amount of the voids 224B filled ispreferably as large as possible. This is to enhance the bonding propertyof the negative electrode active material layer 22B.

In order to suppress adverse effects on the performance of the secondarybattery by the whisker-like fine projections (not shown) on the exposedsurfaces of the uppermost layers of the negative electrode activematerial particles 221, the negative electrode active material layer 22Bmay include the metal material 226 in the gaps 225. In particular, whenthe negative electrode active material particles 221 are formed by avapor phase method, whisker-like fine projections occur at theirsurfaces and gaps 225 are formed between the projections. The gaps 225increases the surface area of the negative electrode active materialparticles 221 as well as the amount of the irreversible coatings formedon their surfaces, possibly resulting in a decrease in extent ofcharge/discharge reaction. Thus, to suppress a decrease in extent ofcharge/discharge reaction, the gaps 225 are filled with the metalmaterial 226. In this case, it is sufficient if just part of the gaps225 is filled but the amount of the gaps 225 filled is preferably aslarge as possible. This is to further suppress the decrease in extent ofcharge/discharge reaction. As shown in FIGS. 6A and 6B, the metalmaterial 226 is interspersed on the surfaces of the uppermost layers ofthe negative electrode active material particles 221. This shows thatthe above-mentioned fine projections are present at these spots.Naturally, it is not essential that the metal material 226 beinterspersed on the surfaces of the negative electrode active materialparticles 221. The metal material 226 may coat the entire surfaces ofthe particles.

In particular, the metal material 226 in the voids 224B also has afunction of filling the gaps 225 between the individual layers. To bemore specific, when a negative electrode material is deposited byperforming deposition several times, fine protrusions occur on thesurfaces of the negative electrode active material particles 221 eachtime the deposition is conducted. Thus, the metal material 226 fills notonly the voids 224B between the layers but also the gaps 225 of theindividual layers.

Note that FIGS. 5A to 6B illustrate the case in which the negativeelectrode active material particles 221 have a multilayer structure andboth the voids 224A and 224B are present in the negative electrodeactive material layer 22B. Thus, the negative electrode active materiallayer 22B have the voids 224A and 224B filled with the metal material226. In contrast, in the case where the negative electrode activematerial particles 221 have a single layer structure and only the voids224A are present in the negative electrode active material layer 22B,the metal material 226 is present only in the voids 224A of the negativeelectrode active material layer 22B. Naturally, since the gaps 225 occurin both cases, the metal material 226 fills the gaps 225 in both cases.

Separator

The separator 23 isolates the positive electrode 21 and the negativeelectrode 22 from each other and allows lithium ions to pass throughwhile preventing shorting of the electrical current caused by thecontact between the electrodes. The separator 23 is impregnated with theabove-mentioned electrolyte which is a liquid electrolyte (electrolyticsolution). The separator 23 is formed of a porous film composed of asynthetic resin or a ceramic, for example, or may be a laminateconstituted by two or more types of porous films. Examples of thesynthetic resin include polytetrafluoroethylene, polypropylene, andpolyethylene.

Operation of the Secondary Battery

When the secondary battery is being charged, lithium ions are releasedfrom the positive electrode 21 and occluded in the negative electrode 22via the electrolytic solution impregnating the separator 23, forexample. In contrast, when the secondary battery is being discharged,lithium ions are released from the negative electrode 22 and occluded inthe positive electrode 21 via the electrolytic solution impregnating theseparator 23, for example.

Method for Producing the Secondary Battery

The secondary battery is produced by the following process, for example.

First, the positive electrode 21 is prepared. To begin with, a positiveelectrode active material is mixed with a positive electrode binder, apositive electrode conductant agent, and the like as needed to prepare apositive electrode mix, and the positive electrode mix is dispersed inan organic solvent to prepare a paste-type positive electrode mixslurry. Then the positive electrode mix slurry is evenly applied on bothsides of the positive electrode collector 21A and dried to form thepositive electrode active material layers 21B. Lastly, the positiveelectrode active material layers 21B are press-formed using a roll pressmachine or the like under heating if necessary. In this case,press-forming may be repeated several times.

Then the negative electrode 22 is prepared by the same process as thepositive electrode 21 described above. That is, a negative electrodeactive material is mixed with a negative electrode binder, a negativeelectrode conductant agent, and the like as needed to prepare a negativeelectrode mix, and the negative electrode mix is dispersed in an organicsolvent to prepare a paste-type negative electrode mix slurry. Then thenegative electrode mix slurry is evenly applied on both sides of thenegative electrode collector 22A to form the negative electrode activematerial layers 22B and the negative electrode active material layers22B are press-formed.

The negative electrode 22 may be prepared by a process different fromthat of the positive electrode 21. In such a case, a plurality ofnegative electrode active material particles are first formed bydepositing a negative electrode material on both sides of the negativeelectrode collector 22A by using a vapor phase method such as a vapordeposition method. Then, if necessary, an oxide-containing film isformed by a liquid phase method such as a liquid phase precipitationmethod, a metal material is formed by using a liquid phase method suchas an electrolytic plating method, or both the oxide-containing film andthe metal material are formed to prepare the negative electrode activematerial layers 22B.

Lastly, the secondary battery is assembled using the positive electrode21 and the negative electrode 22. First, the positive electrode lead 25is attached to the positive electrode collector 21A by welding or thelike and the negative electrode lead 26 is attached to the negativeelectrode collector 22A by welding or the like. Then, the positiveelectrode 21 and the negative electrode 22 are laminated with theseparator 23 therebetween and wound to form the wound electrode body 20.The center pin 24 is inserted into the center of the winding.Subsequently, the wound electrode body 20 is housed inside the batterycan 11 while being sandwiched between the pair of isolators 12 and 13.In this case, a tip of the positive electrode lead 25 is attached to thesafety valve mechanism 15 by welding or the like and a tip of thenegative electrode lead 26 is attached to the battery can 11 by weldingor the like. Then the electrolytic solution is poured into the batterycan 11 to impregnate the separator 23. Lastly, the battery lid 14, thesafety valve mechanism 15, and the thermosensitive resistor 16 arecaulked at the open end of the battery can 11 through the gasket 17.Thus, the secondary battery shown in FIGS. 1 to 6B is made.

With the first secondary battery, since the electrolyte (electrolyticsolution) described above is incorporated, decomposition reaction of theelectrolytic solution during charge/discharge operation can besuppressed in the case where the capacity of the negative electrode 22is indicated by the occlusion and release of lithium ions. As a result,the cycle characteristics and the storage characteristics improve.

In particular, the cycle characteristics and the storage characteristicsimprove when a metal-based material advantageous for achieving highercapacities is used as the negative electrode active material of thenegative electrode 22. Thus higher effects can be obtained when comparedto the cases where carbon materials and the like are used.

Other effects exhibited by the first secondary battery are the same asthose associated with the electrolyte.

2-2. Second Secondary Battery

A second secondary battery is a lithium metal secondary battery in whichthe capacity of the negative electrode is indicated by precipitation anddissolution of lithium metal. This secondary battery has the samestructure as the first secondary battery except that the negativeelectrode active material layer 22B is composed of lithium metal, and isproduced by the same process as the first secondary battery.

The secondary battery uses lithium metal as the negative electrodeactive material so that a higher energy density can be obtained. Thenegative electrode active material layers 22B may be present from thetime of assembly or may be absent at the time of assembly so that theycan be formed by lithium metal deposited during charging operation. Thenegative electrode active material layer 22B may be used as a collectorso that the negative electrode collector 22A can be omitted.

When the secondary battery is being charged, for example, lithium ionsare released from the positive electrode 21 and precipitate into lithiumions at the surface of the negative electrode collector 22A through theelectrolytic solution impregnating the separator 23. In contrast, whenthe secondary battery is being discharged, lithium metal elutes from thenegative electrode active material layers 22B by forming lithium ionsand occluded in the positive electrode 21 via the electrolytic solutionimpregnating the separator 23.

In this second secondary battery, the capacity of the negative electrode22 is indicated by the precipitation and dissolution of the lithiummetal and the secondary battery includes the electrolyte (electrolyticsolution) mentioned above. Thus, owing to the effects similar to thoseof the first secondary battery, the cycle characteristics and thestorage characteristics can be improved. Other advantages of thesecondary battery are the same as those of the first secondary battery.

2-3. Third Secondary Battery

FIG. 7 is an exploded perspective view of a third secondary battery.FIG. 8 is an enlarged view of a cross-section of a wound electrode body30 shown in FIG. 7 taken along line VIII-VIII.

As with the first secondary battery, this secondary battery is a lithiumion secondary battery. Mainly, the wound electrode body 30 to which apositive electrode lead 31 and a negative electrode lead 32 are attachedis housed in a film package member 40. A battery structure that usessuch a film package member 40 is called a laminate film type.

The positive electrode lead 31 and the negative electrode lead 32 extendin the same direction from the interior of the film package member 40toward the exterior, for example. However, the positions where thepositive electrode lead 31 and the negative electrode lead 32 areprovided relative to the wound electrode body 30 and the direction inwhich the positive electrode lead 31 and the negative electrode lead 32extend are not particularly limited. The positive electrode lead 31 iscomposed of, for example, aluminum or the like, and the negativeelectrode lead 32 is composed of, for example, copper, nickel, stainlesssteel, or the like. These materials are, for example, thin-plate-shapedor mesh-shaped.

The film package member 40 is, for example, a laminate film including afusion bonding layer, a metal layer, and a surface-protecting layerstacked in this order. In this case, outer peripheral portions of fusionbonding layers of two films are bonded to each other by fusion-bondingor with an adhesive while arranging the fusion bonding layers to facethe wound electrode body 30. The fusion bonding layer is, for example, afilm composed of polyethylene, polypropylene, or the like. The metallayer is, for example, an aluminum foil or the like. Thesurface-protecting layer may be, for example a film composed of nylon,polyethylene terephthalate, or the like.

In particular, the film package member 40 is preferably an aluminumlaminate film including a polyethylene film, an aluminum foil, and anylon film stacked in that order. The film package member 40 may be alaminate film having another laminate structure, a polymer film such aspolypropylene, or a metal film instead of the aluminum laminate film.

Contact films 41 for preventing entry of outside air are insertedbetween the film package member 40 and the positive electrode lead 31and between the film package member 40 and the negative electrode lead32. The contact films 41 are composed of a material having adhesivenessto the positive electrode lead 31 and the negative electrode lead 32.Examples of such a material include polyolefin resins such aspolyethylene, polypropylene, modified polyethylene, and modifiedpolypropylene.

The wound electrode body 30 includes a positive electrode 33 and anegative electrode 34 laminated with a separator 35 and an electrolytelayer 36 therebetween and its outermost periphery is protected with aprotection tape 37. The positive electrode 33 includes, for example, apositive electrode collector 33A and positive electrode active materiallayers 33B formed on both sides of the positive electrode collector 33A.The structures of the positive electrode collector 33A and the positiveelectrode active material layers 33B are the same as those of thepositive electrode collector 21A and the positive electrode activematerial layers 21B of the first secondary battery, respectively. Thenegative electrode 34 includes, for example, a negative electrodecollector 34A and negative electrode active material layers 34B formedon both sides of the negative electrode collector 34A. The structures ofthe negative electrode collector 34A and the negative electrode activematerial layers 34B are the same as those of the negative electrodecollector 22A and the negative electrode active material layers 22B ofthe first secondary battery, respectively.

The structure of the separator 35 is the same as that of the separator23 of the first secondary battery.

An electrolyte layer 36 is constituted by an electrolytic solutionsupported on a polymer compound and may contain other materials such asvarious additives if necessary. The electrolyte layer 36 is a gel-typeelectrolyte. A gel-type electrolyte is preferred since a high ionconductivity (e.g., 1 mS/cm or more at room temperature) can be obtainedand the leakage of the electrolytic solution can be prevented.

The polymer compound may be at least one selected from the followingpolymer materials: polyacrylonitrile, polyvinylidene fluoride,polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide,polypropylene oxide, polyphosphazene, polysiloxane, polyvinyl fluoride,polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate,polyacrylic acid, polymethacrylic acid, styrene-butadiene rubber,nitrile-butadiene rubber, polystyrene, polycarbonate, and a copolymer ofvinylidene fluoride and hexafluoropyrene. These may be used alone or incombination. Among these, polyvinylidene fluoride or a copolymer ofvinylidene fluoride and hexafluoropyrene are preferred. This is becausethey are electrochemically stable.

The composition of the electrolytic solution is the same as thecomposition of the electrolytic solution of the first secondary battery.Note that for the electrolyte layer 36 which is a gel-type electrolyte,the “solvent” of the electrolytic solution represents a wide conceptincluding not only a liquid solvent but also those solvents which haveion conductivity that can achieve dissociation of the electrolyte salt.Thus, when a polymer compound having ion conductivity is used, thatpolymer compound is included in the solvent.

Alternatively, the electrolytic solution can be directly used instead ofthe electrolyte layer 36 of a gel type in which the electrolyticsolution is supported on the polymer compound. In this case, theseparator 35 is impregnated with the electrolytic solution.

When the secondary battery is being charged, lithium ions are releasedfrom the positive electrode 33 and occluded in the negative electrode 34through the electrolyte layer 36, for example. When the secondarybattery is being discharged, lithium ions are released from the negativeelectrode 34 and occluded in the positive electrode 33 through theelectrolyte layer 36, for example.

The secondary battery including the gel-type electrolyte layer 36 isproduced by any of three production methods described below, forexample.

According to a first production method, the positive electrode 33 andthe negative electrode 34 are first made by the same process for makingthe positive electrode 21 and the negative electrode 22 of the firstsecondary battery. To be more specific, the positive electrode activematerial layers 33B are formed on both sides of the positive electrodecollector 33A to produce the positive electrode 33 and the negativeelectrode active material layers 34B are formed on both sides of thenegative electrode collector 34A to form the negative electrode 34. Thena precursor solution containing the electrolytic solution, the polymercompound, and the solvent is prepared and applied on the positiveelectrode 33 and the negative electrode 34. The solvent is evaporated toform the gel-type electrolyte layers 36. Then the positive electrodelead 31 is attached to the positive electrode collector 33A by weldingor the like and the negative electrode lead 32 is attached to thenegative electrode collector 34A by welding or the like. Then thepositive electrode 33 and the negative electrode 34 both provided withthe electrolyte layers 36 are laminated with the separator 35therebetween and wound. The protection tape 37 is attached on theoutermost periphery to prepare the wound electrode body 30. Lastly, thewound electrode body 30 is placed between the two film package members40 and the outer peripheral portions of the film package members 40 arebonded by fusion bonding or the like to enclose the wound electrode body30. During this process, the contact films 41 are inserted between thefilm package member 40 and the positive electrode lead 31 and betweenthe film package member 40 and the negative electrode lead 32. Thus, thesecondary battery shown in FIGS. 7 and 8 is made.

According to a second production method, first, the positive electrodelead 31 is attached to the positive electrode 33 and the negativeelectrode lead 32 is attached to the negative electrode 34. Then thepositive electrode 33 and the negative electrode 34 are laminated withthe separator 35 therebetween and wound. The protection tape 37 isbonded on the outermost periphery to form a wound body which is aprecursor of the wound electrode body 30. Then the wound body is placedbetween the two film package members 40 and the outer peripheralportions are bonded to each other except for the outer puerperalportions along one side so as to place the wound body in the bag-shapedfilm package member 40. Then an electrolyte composition containing theelectrolytic solution, a monomer to be used as a material for thepolymer compound, a polymerization initiator, and if necessary, othermaterials such as a polymerization inhibitor is prepared and poured intothe bag-shaped film package member 40. The open end of the film packagemember 40 is then sealed by fusion bonding or the like. Lastly, themonomer is thermally polymerized into a polymer compound to form thegel-type electrolyte layer 36. Thus, the secondary battery is made.

According to a third production method, first, the wound body isprepared and placed in the bag-shaped film package member 40 as in thesecond production method above except that a separator 35 both sides ofwhich are coated with a polymer compound is used. The polymer compoundcoating the separator 35 is, for example, a polymer (homopolymer,copolymer, or multi-component copolymer) containing vinylidene fluoride.Specific examples thereof include polyvinylidene fluoride, a binarycopolymer containing vinylidene fluoride and hexafluoropropylene, and atertiary copolymer containing vinylidene fluoride, andhexafluoropropylene, chlorotrifluoroethylene. The polymer compound maycontain one or more other polymer compounds in addition to the polymercontaining vinylidene fluoride. Then an electrolytic solution isprepared and poured into the film package member 40. The open end of thefilm package member 40 is sealed by fusion bonding or the like. Lastly,the film package member 40 is heated under load to allow the separator35 to adhere to the positive electrode 33 and the negative electrode 34through the polymer compound. As a result, the electrolytic solutionimpregnates the polymer compound and the polymer compound gels to formthe electrolyte layer 36, thereby ending fabrication of the secondarybattery.

According to the third production example, swelling of the battery issuppressed compared to the first production method. Moreover, accordingto the third production method, the monomer, which is a material for thepolymer compound, the solvent, or the like rarely remains in theelectrolyte layer 36 and the process of forming the polymer compound iscontrolled well compared to the second production method. Thus,sufficient adhesion is achieved between the positive electrode 33, thenegative electrode 34, the separator 35, and the electrolyte layer 36.

In this third secondary battery, the capacity of the negative electrode34 is indicated by the occlusion and release of lithium ions and theelectrolyte layer 36 includes the electrolyte (electrolytic solution)mentioned above. Thus, owing to the effects similar to those of thefirst secondary battery, the cycle characteristics and the storagecharacteristics can be improved. Other advantages of the secondarybattery are the same as those of the first secondary battery. The thirdsecondary battery does not have to have the same structure as the firstsecondary battery and may have the same structure as the secondsecondary battery.

EXAMPLES

Examples of the present application will now be described in detail.

Experimental Examples 1-1 to 1-22

A cylindrical lithium ion secondary battery shown in FIGS. 1 and 2 wasprepared by the following process.

First, the positive electrode 21 was made. First, lithium carbonate(Li₂CO₃) and cobalt carbonate (CoCO₃) were mixed at a molar ratio of0.5:1 and baked in air at 900° C. for 5 hours to obtain a lithium-cobaltcomplex oxide (LiCoO₂). Then 91 parts by mass of LiCoO₂ serving as apositive electrode active material, 6 parts by mass of graphite servingas a positive electrode conductant agent, and 3 parts by mass ofpolyvinylidene fluoride serving as a positive electrode binder weremixed to prepare a positive electrode mix. The positive electrode mixwas dispersed into N-methyl-2-pyrrolidone to prepare a paste-typepositive electrode mix slurry. Then the positive electrode mix slurrywas evenly applied on both sides of the positive electrode collector 21Aby using a coating device and dried to form the positive electrodeactive material layers 21B. A band-shaped aluminum foil (thickness=20μm) was used as the positive electrode collector 21A. Lastly, thepositive electrode active material layers 21B were press-formed using aroll press machine.

Next, the negative electrode 22 was made. First, 90 parts by mass ofsynthetic graphite serving as a negative electrode active material and10 parts by mass of polyvinylidene fluoride serving as a negativeelectrode binder were mixed to prepare a negative electrode mix. Thenthe negative electrode mix was dispersed into N-methyl-2-pyrrolidone toprepare a paste-type negative electrode mix slurry. Then the negativeelectrode mix slurry was evenly applied on both sides of the negativeelectrode collector 22A by using a coating device and dried to form thenegative electrode active material layers 22B. A band-shapedelectrolytic copper foil (thickness=15 μm) was used as the negativeelectrode collector 22A. Lastly, the negative electrode active materiallayers 22B were press-formed using a roll press machine.

Next, an electrolytic solution, i.e., a liquid electrolyte, wasprepared. First, ethylene carbonate (EC), dimethyl carbonate (DMC), anester compound or the like, an anhydrous compound, and if needed, aphosphoric acid compound were mixed to prepare a solvent. The EC and DMCcontents were adjusted to a weight ratio (EC:DMC) of 30:70. The type andthe contents of the ester compound or the like and the anhydrouscompound in the solvent and presence or absence of the phosphoric acidcompound are shown in Table 1. When the phosphoric acid compound wasused, the content thereof in the solvent was set to 0.01 wt %. Thenlithium hexafluorophosphate (LiPF6) serving as an electrolyte salt wasdissolved in the solvent. The electrolyte salt content was 1 mol/kgrelative to the solvent.

Lastly, a secondary battery was assembled using the positive electrode21, the negative electrode 22, and the electrolytic solution. First, thepositive electrode lead 25 was welded to the positive electrodecollector 21A and the negative electrode lead 26 was welded to thenegative electrode collector 22A. Then, the positive electrode 21 andthe negative electrode 22 were laminated with the separator 23therebetween and wound to form the wound electrode body 20. The centerpin 24 was inserted into the center of the winding. A micro porouspolypropylene film (thickness=25 μm) was used as the separator 23.Subsequently, the wound electrode body 20 was housed inside the batterycan 11 composed of nickel-plated iron while being sandwiched between thepair of isolators 12 and 13. During this operation, the safety valvemechanism 15 was welded to the positive electrode lead 25 and thenegative electrode lead 26 was welded to the battery can 11. Then theelectrolytic solution was poured into the battery can 11 by a pressurereduction technique to impregnate the separator 23. Lastly, the batterylid 14, the safety valve mechanism 15, and the thermosensitive resistor16 were fixed at the open end portion of the battery can 11 by caulkingthrough the gasket 17. Thus, the cylindrical secondary battery was made.In making this secondary battery, the thickness of the positiveelectrode active material layers 21B was adjusted so that lithium metaldoes not precipitate on the negative electrode 22 at the time of fullcharge.

Experimental Examples 1-23 to 1-31

As shown in Table 2, the same process as Experimental Examples 1-1 to1-20 was conducted except that the ester compound or the like and theanhydrous compound were not used in combination.

The cycle characteristics and the storage characteristics of thesecondary batteries of Experimental Examples 1-1 to 1-31 were studied.The obtained results are shown in Tables 1 and 2.

In studying the cycle characteristics, two cycles of charge/dischargeoperation were conducted in a 23° C. atmosphere and then the dischargecapacity of the second cycle was measured. Next, charge/dischargeoperation was repeated in the same atmosphere until the total number ofcycles reached 100, and the discharge capacity of the 100th cycle wasmeasured. Lastly, the cycle discharge capacity retention rate(%)=(discharge capacity of 100th cycle/discharge capacity of the 2ndcycle)×100 was calculated. During the charging operation,constant-current constant-voltage charging was conducted at a 0.2 Ccurrent up to the upper limit voltage of 4.2 V. During the dischargingoperation, constant-current constant-voltage discharge was conducted ata 0.2 C current down to a final voltage of 2.5 V. Here, “0.2 C” refersto the current value according to which a theoretical capacity iscompletely discharged in 5 hours.

In studying the storage characteristics, two cycles of charge/dischargeoperation were conducted in a 23° C. atmosphere and then the dischargecapacity before storage was measured. Then, the battery was chargedagain, stored in a thermostat vessel at 80° C. for 10 days, anddischarged in a 23° C. atmosphere to measure the discharge capacityafter storage. Lastly, the storage discharge capacity retention rate(%)=(discharge capacity after storage/discharge capacity beforestorage)×100 was calculated. The conditions for charge/dischargeoperation were the same as those used to study the cyclecharacteristics.

Note that the same process and conditions for studying the cyclecharacteristics and the storage characteristics are used in thefollowing examples also.

TABLE 1 Negative electrode active material: synthetic graphite, Solvent:EC + DMC, Electrolyte salt: LiPF₆ Other solvents Cycle Storage Estercompound Anhydrous Phosphoric acid discharge discharge or the likecompound compound capacity capacity Content Content Content retentionretention Table 1 Type (wt %) Type (wt %) Type (wt %) rate (%) rate (%)Exp. Ex. 1-1 Formula 0.001 Formula 1 — — 82 88 Exp. Ex. 1-2 (1-1) 0.1(4-2) 84 89 Exp. Ex. 1-3 0.2 85 90 Exp. Ex. 1-4 1 86 90 Exp. Ex. 1-5 580 89 Exp. Ex. 1-6 10 79 87 Exp. Ex. 1-7 Formula 0.2 84 89 (2-1) Exp.Ex. 1-8 Formula 86 91 (3-1) Exp. Ex. 1-9 Li₂PFO₃ 84 88 Exp. Ex. 1-10LiPF₂O₂ 85 90 Exp. Ex. 1-11 Formula 0.2 Formula 1 — — 84 89 (1-1) (4-1)Exp. Ex. 1-12 Formula 83 88 (2-1) Exp. Ex. 1-13 Formula 86 90 (3-1) Exp.Ex. 1-14 Li₂PFO₃ 83 88 Exp. Ex. 1-15 LiPF₂O₂ 85 90 Exp. Ex. 1-16 Formula0.2 Formula 1 — — 85 90 (1-1) (5-1) Exp. Ex. 1-17 Formula 84 89 (2-1)Exp. Ex. 1-18 Formula 86 90 (3-1) Exp. Ex. 1-19 Li₂PFO₃ 85 88 Exp. Ex.1-20 LiPF₂O₂ 85 90 Exp. Ex. 1-21 Formula 0.2 + 0.2 Formula 1 — — 86 92(1-1) + (4-2) Formula (3-1) Exp. Ex. 1-22 Formula 0.2 Formula 1 Formula0.01 85 92 (1-1) (4-2) (6-1) Exp. Ex.: Experimental Example

TABLE 2 Negative electrode active material: synthetic graphite, Solvent:EC + DMC, Electrolyte salt: LiPF₆ Other solvents Cycle Storage EsterAnhydrous discharge discharge compound compound capacity capacityContent Content retention retention Table 2 Type (wt %) Type (wt %) rate(%) rate (%) Exp. Ex. 1-23 — — — — 75 81 Exp. Ex. 1-24 Formula (1-1) 0.2— — 77 82 Exp. Ex. 1-25 Formula (2-1) 76 82 Exp. Ex. 1-26 Formula (3-1)78 83 Exp. Ex. 1-27 Li₂PFO₃ 75 82 Exp. Ex. 1-28 LiPF₂O₂ 77 82 Exp. Ex.1-29 — — Formula (4-2) 1 79 85 Exp. Ex. 1-30 Formula (4-1) 78 84 Exp.Ex. 1-31 Formula (5-1) 78 84 Exp. Ex.: Experimental Example

According to the secondary battery that contained synthetic graphite asthe negative electrode active material, the cycle discharge capacityretention rate and the storage discharge capacity retention rate werehigher when the ester compound or the like and the anhydrous compoundwere used in combination than when they were not used in combination. Inparticular, when the ester compound or the like and the anhydrouscompound were used, better results were obtained at an ester compoundcontent of 10 wt % or less and an anhydrous compound content of 1 wt %or less. Better results were also obtained when the phosphoric acidcompound was used with the ester compound or the like and the anhydrouscompound. These results indicate that for the secondary battery, thecycle characteristics and the storage characteristics improve whensynthetic graphite is used as the negative electrode active material andthe solvent of the electrolyte contains the ester compound or the likeand the anhydrous compound.

The significance of using the ester compound or the like and theanhydrous compound in combination will now be explained. The followingcan be derived from the results shown in Tables 1 and 2. When only theester compound or the like is used, both the cycle discharge capacityretention rate and the storage discharge capacity retention rateincrease slightly compared to when none of the ester compound or thelike and the anhydrous compound is used. When only the anhydrouscompound is used, both the cycle discharge capacity retention rate andthe storage discharge capacity retention rate also increase slightlycompared to when none of the ester compound or the like and theanhydrous compound is used. Based on these results, the combined used ofthe ester compound or the like and the anhydrous compound is supposed togive a result which is merely a sum of the results obtained when theyare used separately. In other words, the increase in the cycle dischargecapacity retention rate and the storage discharge capacity retentionrate is supposed to be equal to the total of the increases achieved whenthe ester compound or the like and the anhydrous compound are usedseparately. However, actually, the increase is far higher when the estercompound or the like and the anhydrous compound are used in combinationthan the total of the increases obtained when they are used separately.These results show that when the ester compound or the like and theanhydrous compound are used in combination, synergetic effects cause thecycle discharge capacity retention rate and the storage dischargecapacity retention rate to significantly increase, which is a specialadvantage. Thus, the significance of using the ester compound or thelike and the anhydrous compound in combination is that an advantage notpredictable from the results obtained by separately using the estercompound of the like and the anhydrous compound can be obtained.

Experimental Examples 2-1 to 2-12

As shown in Table 3, the same process as Experimental Examples 1-3 and1-23 was conducted except that the composition of the solvent waschanged. In these examples, vinylene carbonate (VC), bis(fluoromethyl)carbonate (DFDMC), and 4-fluoro-1,3-dioxolan-2-one (FEC) were used.Moreover, trans-4,5-difluoro-1,3-dioxolan-2-one (TDFEC) andcis-4,5-difluoro-1,3-dioxolan-2-one (CDFEC) were used. Propene sultone(PRS), succinic anhydride (SA), and sulfobenzoic anhydride (SBAH) werealso used. The VC content, the PRS content, the SA content, and the SBAHcontent in the solvent were 1 wt % each and the DFDMC content, the FECcontent, the TDFEC content, and the CDFEC content in the solvent were 5wt % each. The cycle characteristics and the storage characteristics ofthe secondary batteries of Experimental Examples 2-1 to 2-12 werestudied. The obtained results are shown in Table 3.

TABLE 3 Negative electrode active material: synthetic graphite, Solvent:EC + DMC, Electrolyte salt: LiPF₆ Other solvents Cycle Storage EsterAnhydrous discharge discharge compound compound capacity capacityContent Content retention retention Table 3 Solvent Type (wt %) Type (wt%) rate (%) rate (%) Exp. Ex. 2-1 VC Formula 0.2 Formula 1 89 91 Exp.Ex. 2-2 DFDMC (1-1) (4-2) 89 88 Exp. Ex. 2-3 FEC 90 92 Exp. Ex. 2-4TDFEC 91 91 Exp. Ex. 2-5 CDFEC 91 91 Exp. Ex. 2-6 VC + FEC 92 94 Exp.Ex. 2-7 FEC + PRS 92 94 Exp. Ex. 2-8 FEC + SA 93 93 Exp. Ex. 2-9 FEC +SBAH 93 94 Exp. Ex. 2-10 VC — — — — 78 83 Exp. Ex. 2-11 FEC 80 84 Exp.Ex. 2-12 TDFEC 82 84 Exp. Ex.: Experimental Example

The results similar to those shown in Tables 1 and 2 were obtained evenby changing the composition of the solvent. Better results were obtainedwhen VC and the like were used as the solvent than when they were notused. The results indicate that the cycle characteristics and thestorage characteristics of the secondary battery containing syntheticgraphite as a negative electrode active material improve even when thecomposition of the electrolytic solution is changed.

Experimental Examples 3-1 to 3-4

As shown in Table 4, the same process as Experimental Examples 1-3 and1-23 was conducted except that the type of the electrolyte salt waschanged. In these examples, lithium tetrafluoroborate (LiBF₄), acompound represented by formula (12-6), and a lithiumbis(trifluoromethanesulfonyl)imide (LiN(CF₃SO₂)₂) (LiTFSI) were used asthe electrolyte salt. The LiPF₆ content was set to 0.9 mol/kg withrespect to the solvent and the content of LiBF₄ or the like was set to0.1 mol/kg with respect to the solvent. The cycle characteristics andthe storage characteristics of the secondary batteries of ExperimentalExamples 3-1 to 3-4 were studied. The obtained results are shown inTable 4.

TABLE 4 Negative electrode active material: synthetic graphite, Solvent:EC + DMC, Electrolyte salt: LiPF₆ Other solvents Cycle Storage EsterAnhydrous discharge discharge compound compound capacity capacityContent Content Electrolyte retention retention Table 4 Type (wt %) Type(wt %) salt rate (%) rate (%) Exp. Ex. 3-1 Formula 0.2 Formula 1 LiBF₄85 92 Exp. Ex. 3-2 (1-1) (4-2) (12-6) 86 93 Exp. Ex. 3-3 LiTFSI 88 92Exp. Ex. 3-4 — — — — Formula 79 83 (12-6) Exp. Ex.: Experimental Example

The results similar to those shown in Tables 1 and 2 were obtained evenby changing the type of the electrolyte salt. Better results wereobtained when LiBF₄ or the like was used as the electrolyte salt thanwhen not. The results indicate that the cycle characteristics and thestorage characteristics of the secondary battery containing syntheticgraphite as a negative electrode active material improve even when thetype of the electrolyte salt is changed.

Experimental Examples 4-1 to 4-31

The same process as Experimental Examples 1-1 to 1-31 was conductedexcept that the negative electrode 22 was made by using silicon as thenegative electrode active material and diethyl carbonate (DEC) was usedas the solvent instead of DMC. In making the negative electrode 22,silicon was deposited on the surfaces of the negative electrodecollector 22A by a vapor deposition method (electron beam depositionmethod) to form the negative electrode active material layers 22Bcontaining negative electrode active material particles. In theseexamples, the deposition step was repeated 10 times to make a negativeelectrode active material layer 22B having a total thickness of 6 μm.The cycle characteristics and the storage characteristics of thesecondary batteries of Experimental Examples 4-1 to 4-31 were studied.The obtained results are shown in Tables 5 and 6.

TABLE 5 Negative electrode active material: silicon, Solvent: EC + DEC,Electrolyte salt: LiPF₆ Other solvents Cycle Storage Ester compoundAnhydrous Phosphoric acid discharge discharge or the like compoundcompound capacity capacity Content Content Content retention retentionTable 5 Type (wt %) Type (wt %) Type (wt %) rate (%) rate (%) Exp. Ex.4-1 Formula 0.001 Formula 1 — — 58 88 Exp. Ex. 4-2 (1-1) 0.1 (4-2) 61 89Exp. Ex. 4-3 0.2 61 90 Exp. Ex. 4-4 1 60 90 Exp. Ex. 4-5 5 58 89 Exp.Ex. 4-6 10 55 87 Exp. Ex. 4-7 Formula 0.2 59 88 (2-1) Exp. Ex. 4-8Formula 62 91 (3-1) Exp. Ex. 4-9 Li₂PFO₃ 60 88 Exp. Ex. 4-10 LiPF₂O₂ 6189 Exp. Ex. 4-11 Formula 0.2 Formula 1 — — 60 89 (1-1) (4-1) Exp. Ex.4-12 Formula 59 89 (2-1) Exp. Ex. 4-13 Formula 62 90 (3-1) Exp. Ex. 4-14Li₂PFO₃ 60 88 Exp. Ex. 4-15 LiPF₂O₂ 62 89 Exp. Ex. 4-16 Formula 0.2Formula 1 — — 62 90 (1-1) (5-1) Exp. Ex. 4-17 Formula 61 89 (2-1) Exp.Ex. 4-18 Formula 63 92 (3-1) Exp. Ex. 4-19 Li₂PFO₃ 60 88 Exp. Ex. 4-20LiPF₂O₂ 62 89 Exp. Ex. 4-21 Formula 0.2 + 0.2 Formula 1 — — 63 92(1-1) + (4-2) Formula (3-1) Exp. Ex. 4-22 Formula 0.2 Formula 1 Formula0.01 62 92 (1-1) (4-2) (6-1) Exp. Ex.: Experimental Example

TABLE 6 Negative electrode active material: silicon, Solvent: EC + DEC,Electrolyte salt: LiPF₆ Other solvents Cycle Storage Ester Anhydrousdischarge discharge compound compound capacity capacity Content Contentretention retention Table 6 Type (wt %) Type (wt %) rate (%) rate (%)Exp. Ex. 4-23 — — — — 40 81 Exp. Ex. 4-24 Formula (1-1) 0.2 — — 42 82Exp. Ex. 4-25 Formula (2-1) 41 82 Exp. Ex. 4-26 Formula (3-1) 44 83 Exp.Ex. 4-27 Li₂PFO₃ 40 82 Exp. Ex. 4-28 LiPF₂O₂ 42 82 Exp. Ex. 4-29 — —Formula (4-2) 1 55 85 Exp. Ex. 4-30 Formula (4-1) 54 84 Exp. Ex. 4-31Formula (5-1) 54 84 Exp. Ex.: Experimental Example

Results similar to those shown in Tables 1 and 2 were obtained from thesecondary batteries that use silicon as the negative electrode activematerial. That is, the cycle discharge capacity retention rate and thestorage discharge capacity retention rate were higher when the estercompound or the like and the anhydrous compound were used in combinationthan when they were not. These results indicate that for the secondarybattery, the cycle characteristics and the storage characteristicsimprove when silicon is used as the negative electrode active materialand the solvent of the electrolyte contains the ester compound or thelike and the anhydrous compound.

Experimental Examples 5-1 to 5-12

As shown in Table 7, the same process as Experimental Examples 2-1 to2-12 was conducted except that silicon was used as the negativeelectrode active material as with Experimental Examples 4-1 to 4-31. Thecycle characteristics and the storage characteristics of the secondarybatteries of Experimental Examples 5-1 to 5-12 were studied. Theobtained results are shown in Table 7.

TABLE 7 Negative electrode active material: silicon, Solvent: EC + DEC,Electrolyte salt: LiPF₆ Other solvents Cycle Storage Anhydrous dischargedischarge Ester compound compound capacity capacity Content Contentretention retention Table 7 Solvent Type (wt %) Type (wt %) rate (%)rate (%) Exp. Ex. 5-1 VC Formula 0.2 Formula 1 80 93 Exp. Ex. 5-2 DFDMC(1-1) (4-2) 72 92 Exp. Ex. 5-3 FEC 72 94 Exp. Ex. 5-4 TDFEC 85 94 Exp.Ex. 5-5 CDFEC 85 94 Exp. Ex. 5-6 VC + FEC 78 94 Exp. Ex. 5-7 FEC + PRS72 95 Exp. Ex. 5-8 FEC + SA 73 95 Exp. Ex. 5-9 FEC + SBAH 74 95 Exp. Ex.5-10 VC — — — — 70 84 Exp. Ex. 5-11 FEC 60 84 Exp. Ex. 5-12 TDFEC 76 84Exp. Ex.: Experimental Example

The results similar to those shown in Tables 5 and 6 were obtained evenby changing the composition of the solvent. The results indicate thatthe cycle characteristics and the storage characteristics of thesecondary battery containing silicon as a negative electrode activematerial improve even when the composition of the solvent is changed.

Experimental Examples 6-1 to 6-4

As shown in Table 8, the same process as Experimental Examples 3-1 to3-4 was conducted except that silicon was used as the negative electrodeactive material as with Experimental Examples 4-1 to 4-31. The cyclecharacteristics and the storage characteristics of the secondarybatteries of Experimental Examples 6-1 to 6-4 were studied. The obtainedresults are shown in Table 8.

TABLE 8 Negative electrode active material: silicon, Solvent: EC + DEC,Electrolyte salt: LiPF₆ Other solvents Cycle Storage Ester Anhydrousdischarge discharge compound compound capacity capacity Content ContentElectrolyte retention retention Table 8 Type (wt %) Type (wt %) saltrate (%) rate (%) Exp. Ex. 6-1 Formula 0.2 Formula 1 LiBF₄ 61 91 Exp.Ex. 6-2 (1-1) (4-2) Formula 62 92 (12-6) Exp. Ex. 6-3 LiTFSI 64 90 Exp.Ex. 6-4 — — — — Formula 50 83 (12-6) Exp. Ex.: Experimental Example

The results similar to those shown in Tables 5 and 6 were obtained evenby changing the composition of the electrolyte salt. The resultsindicate that the cycle characteristics and the storage characteristicsof the secondary battery containing silicon as a negative electrodeactive material improve even when the composition of the electrolytesalt is changed.

Experimental Examples 7-1 to 7-4

The same processes as Experimental Examples 4-2, 5-3, 4-23, and 5-11were conducted except that the negative electrode 22 was prepared byusing a SnCoC-containing material as the negative electrode activematerial.

The negative electrode 22 was made as follows. First, a cobalt powderand a tin powder were alloyed to form a cobalt/tin alloy powder. Acarbon powder was added thereto and the resulting mixture was dry-mixed.Then 10 g of the mixture was placed in a reactor of a planetary ballmill produced by Ito Seisakusho Co., Ltd., along with about 400 g ofsteel balls having a diameter of 9 mm. After the atmosphere in thereactor was purged with argon, a cycle of 10 minutes of operation at 250rotations per minute and 10 minutes of rest was repeated until the totaltime of operation was 20 hours. Then the reactor was cooled to roomtemperature and the SnCoC-containing material was discharged andfiltered through a 280-mesh screen to remove coarse particles.

The composition of the obtained SnCoC-containing material was analyzed.It was found that the tin content was 49.5 mass %, the cobalt contentwas 29.7 mass %, the carbon content was 19.8 mass %, and the ratio ofthe cobalt to the total of the tin and cobalt (Co/(Sn+Co)) was 37.5 mass%. The tin and cobalt contents were measured by inductively coupledplasma (ICP) spectroscopy and the carbon content was measured with acarbon/sulfur analyzer. The SnCoC-containing material was also analyzedby X-ray diffraction. A diffraction peak having a half-width value of1.0° or more in terms of 2θ diffraction angle was found in the range ofdiffraction angle 2θ=20° to 50°. The SnCoC-containing material wasfurther analyzed by XPS and peak P1 was obtained as shown in FIG. 9.When the peak P1 was analyzed, peak P2 of surface-contaminating carbonand peak P3 of C1s in the SnCoC-containing material at thelower-energy-side of the peak P2 (the region lower than 284.5 eV) wereobtained. These results confirmed that carbon in the SnCoC-containingmaterial is bonded to other elements.

After the SnCoC-containing material was obtained, 80 parts by mass ofthe SnCoC-containing material serving as a negative electrode activematerial was mixed with 8 parts by mass of polyvinylidene fluorideserving as a negative electrode binder and 11 parts by mass of graphiteand 1 part by weight of acetylene black serving as negative electrodeconductant agents to prepare a negative electrode mix. Then the negativeelectrode mix was dispersed into N-methyl-2-pyrrolidone to prepare apaste-type negative electrode mix slurry. Lastly, the negative electrodemix slurry was evenly applied on both sides of the negative electrodecollector 22A by using a coating device and dried to form the negativeelectrode active material layers 22B. The negative electrode activematerial layers 22B were then press-formed with a roll press machine.

The cycle characteristics and the storage characteristics of thesecondary batteries of Experimental Examples 7-1 to 7-4 were studied.The obtained results are shown in Table 9.

TABLE 9 Negative electrode active material: SnCoC-containing material,Solvent: EC + DEC, Electrolyte salt: LiPF₆ Other solvents Cycle StorageAnhydrous discharge discharge Ester compound compound capacity capacityContent Content retention retention Table 9 Solvent Type (wt %) Type (wt%) rate (%) rate (%) Exp. Ex. 7-1 — Formula (1-1) 0.1 Formula 1 85 82Exp. Ex. 7-2 FEC (4-2) 92 86 Exp. Ex. 7-3 — — — — — 70 76 Exp. Ex. 7-4FEC 90 84 Exp. Ex.: Experimental Example

The results similar to those shown in Tables 5 to 7 were obtained fromthe secondary batteries that use the SnCoC-containing material as thenegative electrode active material. That is, the cycle dischargecapacity retention rate and the storage discharge capacity retentionrate were higher when the ester compound or the like and the anhydrouscompound were used in combination than when they were not. These resultsindicate that for the secondary battery, the cycle characteristics andthe storage characteristics improve when the SnCoC-containing materialis used as the negative electrode active material and the solvent of theelectrolytic solution contains the ester compound or the like and theanhydrous compound.

Experimental Examples 8-1 to 8-6, 9-1, 9-2, 10-1, and 10-2

As shown in Tables 10 to 12, the same processes as Experimental Examples4-2, 5-3, 5-4, 4-23, 5-11, and 5-12 were conducted except that at leastone of an oxide-containing film and a metal material was formed.

In the examples in which the oxide-containing film was formed, negativeelectrode active material particles were formed first and then siliconoxide (SiO₂) was precipitated on the surfaces of the negative electrodeactive material particles by a liquid phase precipitation method. Inthese examples, the negative electrode collector 22A on which thenegative electrode active material particles were formed was immersedfor 3 hours in a solution prepared by dissolving boron serving as ananion scavenger in hydrofluorosilicic acid to allow silicon oxide toprecipitate on the surfaces of the negative electrode active materialparticles and then washed with washer, followed by vacuum drying.

In forming the metal material, a cobalt (Co) plating film was depositedby an electroplating method in voids between the negative electrodeactive material particles while energizing and supplying air to theplating solution. In this case, a cobalt plating solution produced byJapan Pure Chemical Co., Ltd. was used as the plating solution, thecurrent density was set to 2 A/dm² to 5 A/dm², and the plating rate wasset to 10 nm/sec.

The cycle characteristics and the storage characteristics of thesecondary batteries of Experimental Examples 8-1 to 8-6, 9-1, 9-2, 10-1,and 10-2 were studied. The obtained results are shown in Tables 10 to12.

TABLE 10 Negative electrode active material: silicon, Solvent: EC + DEC,Electrolyte salt: LiPF₆ Other solvents Cycle Storage Ester Anhydrousdischarge discharge compound compound Oxide- capacity capacity ContentContent containing Metal retention retention Table 10 Solvent Type (wt%) Type (wt %) film material rate (%) rate (%) Exp. — Formula 0.1Formula 1 SiO₂ Co 88 80 Ex. 8-1 (1-1) (4-2) Exp. FEC 91 88 Ex. 8-2 Exp.TDFEC 92 92 Ex. 8-3 Exp. — — — — — SiO₂ Co 86 75 Ex. 8-4 Exp. FEC 89 84Ex. 8-5 Exp. TDFEC 88 90 Ex. 8-6 Exp. Ex.: Experimental Example

TABLE 11 Negative electrode active material: silicon, Solvent: EC + DEC,Electrolyte salt: LiPF₆ Other solvents Cycle Storage Ester Anhydrousdischarge discharge compound compound Oxide- capacity capacity ContentContent containing Metal retention retention Table 11 Type (wt %) Type(wt %) film material rate (%) rate (%) Exp. Ex. 9-1 Formula 0.1 Formula1 SiO₂ — 88 78 (1-1) (4-2) Exp. Ex. 9-2 — — — — SiO₂ — 86 70 Exp. Ex.:Experimental Example

TABLE 12 Negative electrode active material: silicon, Solvent: EC + DEC,Electrolyte salt: LiPF₆ Other solvents Cycle Storage Ester Anhydrousdischarge discharge compound compound Oxide- capacity capacity ContentContent containing Metal retention retention Table 12 Type (wt %) Type(wt %) film material rate (%) rate (%) Exp. Ex. 10-1 Formula 0.1 Formula1 — Co 88 76 (1-1) (4-2) Exp. Ex. 10-2 — — — — — Co 86 65 Exp. Ex.:Experimental Example

The results similar to those shown in Tables 5 to 7 were obtained evenwhen the oxide-containing film and the metal material were formed. Inparticular, better results were obtained when the oxide-containing filmand the metal material were formed than when they were not formed.Better results were obtained when both the oxide-containing film and themetal material were formed than when only one of them was formed. Whenone of the oxide-containing film and the metal material was formed,better results were obtained from samples with the oxide-containingfilm. These results show that, according to the secondary battery, thecycle characteristics and the storage characteristics improve even whenthe oxide-containing film and the metal material are formed.

The results shown in Tables 1 to 12 show that, according to thesecondary battery, the solvent of the electrolytic solution contains acombination of an ester compound or the like and an anhydrous compound.Thus, the cycle characteristics and the storage characteristics can beimproved irrespective of the type of the negative electrode activematerial, the solvent composition, the electrolyte salt composition, orthe absence or presence of the oxide-containing film and the metalmaterial.

In such a case, the rates of increase in the cycle discharge capacityretention rate and the storage discharge capacity retention rate weregreater when the metal-based materials (silicon and SnCoC-containingmaterial) were used than when the carbon material (synthetic graphite)was used as the negative electrode active material. This shows thathigher effects can be obtained by using the metal-based material than byusing the carbon material. These results are obtained presumably becausewhen a metal-base material advantageous for increasing the capacity isused as the negative electrode active material, the electrolyticsolution is more easily decomposed than when a carbon material is usedand thus the effect of suppressing the decomposition of the electrolyticsolution became particularly notable in such cases.

Although the present invention is described above with reference toembodiments and examples, the present invention is not limited to theembodiments and the examples described above and allows variousmodifications. For example, the usage of the electrolyte is not limitedto secondary batteries and the electrolyte may be used in otherelectrochemical devices. Examples of other usages include capacitors.

In the embodiments and examples described above, lithium ion secondarybatteries and lithium metal secondary batteries are described as thetypes of the secondary batteries. However, the battery type is notlimited to these. The secondary battery can be equally applied to asecondary battery in which the capacity of the negative electrodeincludes the capacity derived from the occlusion and release of lithiumions and the capacity associated with precipitation and dissolution oflithium metal and can be indicated as the sum of these capacities. Insuch a case, a negative electrode material that can occlude and releaselithium ions is used as the negative electrode active material. Thechargeable capacity of the negative electrode material is set to belower than the discharge capacity of the positive electrode.

Although the cases where the battery structure is of a cylindrical typeor a laminate film type and the battery element has a wound structureare described in the embodiments and examples described above, thestructures are not limited to these. The secondary battery describedherein is equally applicable to cases where the battery has a square,coin, or button structure and where the battery element has otherstructures such as a multilayer structure.

In the embodiments and examples described above, cases where lithium isused as the element of the electrode reactant are described but thepresent invention is not limited to these cases. The electrode reactantmay be, for example, other group 1A elements such as sodium (Na) andpotassium (K), group 2A elements such as magnesium and calcium, andother light metals such as aluminum. The advantages of the presentinvention should be obtained irrespective of the type of the electrodereactant. Thus, the same advantages can be obtained even when the typeof the electrode reactant is changed.

In the embodiments and examples above, the contents of the estercompound or the like and the anhydrous compound are described as optimumranges derived from the results of the examples. However, thedescription does not deny the possibility that the contents may beoutside the above-described ranges. In other words, the optimum rangesdescribed above are merely preferable ranges for obtaining theadvantages of the present invention. The contents may be more or lessoutside the above-described ranges as long as the advantages of thepresent invention are obtained.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope and without diminishing itsintended advantages. It is therefore intended that such changes andmodifications be covered by the appended claims.

The application is claimed as follows:
 1. A secondary batterycomprising: a positive electrode; a negative electrode; and anelectrolyte including a solvent and an electrolyte salt, wherein thesolvent contains A and B, A is at least one selected from the groupconsisting of ester compounds represented by formulae (1), estercompounds represented by formulae (2), ester compounds represented byformulae (3), lithium monofluorophosphate (Li₂PFO₃), and lithiumdifluorophosphate (LiPF₂O₂), and B is at least one selected from thegroup consisting of anhydrous compounds represented by formulae (4), andanhydrous compounds represented by formulae (5):

R11 and R13 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof; R12represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond (—O—) and an alkylenegroup, or a halogenated group thereof;

R14 and R16 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof; R15represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof;

R17 and R19 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof; R18represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof;

X21 represents a C2-C4 alkylene group that may be halogenated, a C2-C4alkenylene group that may be halogenated, an arylene group that may behalogenated, or a derivative thereof; and

X22 represents a C2-C4 alkylene group that may be halogenated, a C2-C4alkenylene group that may be halogenated, an arylene group that may behalogenated, or a derivative thereof.
 2. The secondary battery accordingto claim 1, wherein the ester compounds are represented by formulae(1-1), (2-1), and (3-1):


3. The secondary battery according to claim 1, wherein the anhydrouscompounds are represented by formulae (4-1) to (4-22) and (5-1) to(5-20):


4. The secondary battery according to claim 3, wherein the anhydrouscompounds are represented by formulae (4-1), (4-2), and (5-1).
 5. Thesecondary battery according to claim 1, wherein the content of at leastone selected from the ester compounds, lithium monofluorophosphate, andlithium difluorophosphate in the solvent is 0.001 wt % or more and 10 wt% or less.
 6. The secondary battery according to claim 1, wherein thecontent of the anhydrous compound in the solvent is 0.01 wt % or moreand 1 wt % or less.
 7. The secondary battery according to claim 1,wherein the solvent further contains a phosphoric acid compoundrepresented by formula (6):

R31 to R33 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof.
 8. Thesecondary battery according to claim 7, wherein the phosphoric acidcompound is represented by formula (6-1):


9. The secondary battery according to claim 1, wherein the solventfurther contains at least one selected from unsaturated carbonbond-containing cyclic carbonic acid esters represented by formulae (7)to (9), halogenated chain carbonic acid esters represented by formula(10), halogenated cyclic carbonic acid esters represented by formula(11), sultones, and acid anhydrides:

R41 and R42 each represent a hydrogen group or an alkyl group;

R43 to R46 each represent a hydrogen group, an alkyl group, a vinylgroup, or an allyl group and at least one of R43 to R46 is a vinyl groupor an allyl group;

R47 represents an alkylene group;

R51 to R56 each represent a hydrogen group, a halogen group, an alkylgroup, or a halogenated alkyl group and at least one of R51 to R56 is ahalogen group or a halogenated alkyl group; and

R57 to R60 each represent a hydrogen group, a halogen group, an alkylgroup, or a halogenated alkyl group and at least one of R57 to R60 is ahalogen group or a halogenated alkyl group.
 10. The secondary batteryaccording to claim 9, wherein the unsaturated carbon bond-containingcyclic carbonic acid esters are vinylene carbonate, vinyl ethylenecarbonate, and methylene ethylene carbonate, the halogenated chaincarbonic acid esters are fluoromethyl methyl carbonate andbis(fluoromethyl) carbonate, and the halogenated cyclic carbonic acidesters are 4-fluoro-1,3-dioxolan-2-one and4,5-difluoro-1,3-dioxolan-2-one.
 11. The secondary battery according toclaim 1, wherein the electrolyte salt includes at least one selectedfrom lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate(LiBF₄), lithium perchlorate (LiClO₄), lithium hexafluoroarsenate(LiAsF₆), and compounds represented by formulae (12) to (17):

X61 represents a group 1A or 2A element in the short-form periodic tableor aluminum (Al); M61 represents a transition metal or a group 3B, 4B,or 5B element in the short-form periodic table; R61 represents a halogengroup; Y61 represents —C(═O)—R62-C(═O)—, —C(═O)—CR63₂-, or —C(═O)—C(═O)—where R62 represents an alkylene group, a halogenated alkylene group, anarylene group, or a halogenated arylene group, R63 represents an alkylgroup, a halogenated alkyl group, an aryl group, or a halogenated arylgroup, a6 represents an integer of 1 to 4, b6 represents an integer of0, 2, or 4, and c6, d6, m6, and n6 each represent an integer of 1 to 3;

X71 represents a group 1A or 2A element in the short-form periodictable; M71 represents a transition metal or a group 3B, 4B, or 5Belement in the short-form periodic table; Y71 represents—C(═O)—(CR71₂)_(b7)-C(═O)—, —R73₂C—(CR72₂)_(c7)-C(═O)—,—R73₂C—(CR72₂)_(c7-CR)73₂-, —R73₂C—(CR72₂)_(c7)-S(═O)₂—,—S(═O)₂—(CR72₂)_(d7)-S(═O)₂—, or —C(═O)—(CR72₂)_(d7)-S(═O)₂— where R71and R73 each represent a hydrogen group, an alkyl group, a halogengroup, or a halogenated alkyl group and at least one of R71 and R73 is ahalogen group or a halogenated alkyl group, R72 represents a hydrogengroup, an alkyl group, a halogen group, or a halogenated alkyl group,a7, e7, and n7 each represent an integer of 1 or 2, b7 and d7 eachrepresent an integer of 1 to 4, c7 represents an integer of 0 to 4, andf7 and m7 each represent an integer of 1 to 3;

X81 represents a group 1A or 2A element in the short-form periodictable; M81 represents a transition metal or a group 3B, 4B, or 5Belement in the short-form periodic table; Rf represents a C1-C10fluorinated alkyl group or a C1-C10 fluorinated aryl group; Y81represents —C(═O)—(CR81₂)_(d8)-C(═O)—, —R82₂C—(CR81₂)_(d8)-C(═O)—,—R82₂C—(CR81₂)_(d8)-CR82₂-, —R82₂C—(CR81₂)_(d8)-S(═O)₂—,—S(═O)₂—(CR81₂)_(e8)-S(═O)₂—, or —C(═O)—(CR81₂)_(e8)-S(═O)₂— where R81represents a hydrogen group, an alkyl group, a halogen group, or ahalogenated alkyl group, R82 represents a hydrogen group, an alkylgroup, a halogen group, or a halogenated alkyl group and at least one ofR82s is a halogen group or a halogenated alkyl group, a8, f8, and n8each represent an integer of 1 or 2, b8, c8, and e8 each represent aninteger of 1 to 4, d8 represents an integer of 0 to 4, and g8 and m8each represent an integer of 1 to 3;LiN(C_(m)F_(2m+1)SO₂)(C_(n)F_(2n+1)SO₂)  (15) m and n each represent aninteger of 1 or more;

R91 represents a C2-C4 linear or branched perfluoroalkylene group; andLiC(C_(p)F_(2p+1)SO₂)(C_(q)F_(2q+1)SO₂)(C_(r)F_(2r+1)SO₂)  (17) p, q,and r each represent an integer of 1 or more.
 12. The secondary batteryaccording to claim 11, wherein the compounds represented by formula (12)are represented by formulae (12-1) to (12-6), the compounds representedby formula (13) are represented by formulae (13-1) to (13-8), and thecompound represented by formula (14) is represented by formula (14-1):


13. The secondary battery according to claim 1, wherein the negativeelectrode includes, as a negative electrode active material, a carbonmaterial, lithium metal (Li), or a material that contains, as aconstitutional element, at least one metal or semimetal element and thatcan occlude and release an electrode reactant.
 14. The secondary batteryaccording to claim 1, wherein the negative electrode includes, as anegative electrode active material, a material that contains at leastone of silicon (Si) and tin (Sn) as a constitutional element.
 15. Thesecondary battery according to claim 14, wherein the material thatcontains at least one of silicon and tin as the constitutional elementis silicon as a single element or a material that contains tin, cobalt(Co), and carbon (C) as constitutional elements, in the material thatcontains tin, cobalt, and carbon, the carbon content is 9.9 mass % ormore and 29.7 mass % or less and the ratio of the cobalt content to thetotal content of tin and cobalt (Co/(Sn+Co)) is 20 mass % or more and 70mass % or less, and the half width of a diffraction peak obtained byX-ray diffraction is 1.0° or more.
 16. The secondary battery accordingto claim 1, wherein the negative electrode includes a negative electrodeactive material layer including a plurality of negative electrode activematerial particles, the negative electrode active material layer furtherincludes an oxide-containing film coating surfaces of the negativeelectrode active material particles, and the oxide-containing filmcontains at least one selected from a silicon oxide, a germanium (Ge)oxide, and a tin oxide.
 17. The secondary battery according to claim 1,wherein the negative electrode includes a negative electrode activematerial layer including a plurality of negative electrode activematerial particles, the negative electrode active material layer furtherincludes a metal material that contains, as a constitutional element, ametal element that does not alloy with an electrode reactant, the metalmaterial being present in voids inside the negative electrode activematerial layer, and the metal element is at least one selected from iron(Fe), cobalt, nickel (Ni), zinc (Zn), and copper (Cu).
 18. The secondarybattery according to claim 1, wherein the positive electrode and thenegative electrode can occlude and release an electrode reactant and theelectrode reactant is lithium ions.
 19. An electrolyte comprising: asolvent; and an electrolyte salt, wherein the solvent contains A and B,A is at least one selected from the group consisting of ester compoundsrepresented by formulae (1), ester compounds represented by formulae(2), ester compounds represented by formulae (3), lithiummonofluorophosphate, and lithium difluorophosphate, and B is at leastone selected from the group consisting of anhydrous compoundsrepresented by formulae (4), and anhydrous compounds represented byformulae (5):

R11 and R13 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof; R12represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof;

R14 and R16 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof; R15represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof;

R17 and R19 each represent an alkyl group, an alkenyl group, an alkynylgroup, an aryl group, a heterocyclic group, an alkyl, alkenyl, oralkynyl group substituted with an aromatic hydrocarbon group or analicyclic hydrocarbon group, or a halogenated group thereof; R18represents a linear or branched alkylene group, an arylene group, adivalent group containing an arylene group and an alkylene group, aC2-C12 divalent group containing an ether bond and an alkylene group, ora halogenated group thereof;

X21 represents a C2-C4 alkylene group that may be halogenated, a C2-C4alkenylene group that may be halogenated, an arylene group that may behalogenated, or a derivative thereof; and

X22 represents a C2-C4 alkylene group that may be halogenated, a C2-C4alkenylene group that may be halogenated, an arylene group that may behalogenated, or a derivative thereof.
 20. The electrolyte according toclaim 19, wherein the electrolyte is used in a secondary battery.